Title of Invention	LIGHT EMITTING DEVICE, IN PARTICULAR TRAFFIC SIGNAL LIGHT EMITTING DEVICE, WHICH IS COMPOSED OF LIGHT EMITTING DIODES
Abstract	There is disclosed a light emitting device, in particular a traffic signal light emitting device, composed with light emitting diodes (=LEDs) (30), said device having at least one strand (102) with a multiplicity of LEDs (30) connected in series; said strand being adapted to be connected via a current limiting means, substantially to a mains voltage of at least 110V without voltage conversion and without pulse modulation; and having a means for suppressing afterglow of the LEDs (30).

Title of Invention

LIGHT EMITTING DEVICE, IN PARTICULAR TRAFFIC SIGNAL LIGHT EMITTING DEVICE, WHICH IS COMPOSED OF LIGHT EMITTING DIODES

Abstract

There is disclosed a light emitting device, in particular a traffic signal light emitting device, composed with light emitting diodes (=LEDs) (30), said device having at least one strand (102) with a multiplicity of LEDs (30) connected in series; said strand being adapted to be connected via a current limiting means, substantially to a mains voltage of at least 110V without voltage conversion and without pulse modulation; and having a means for suppressing afterglow of the LEDs (30).

Full Text	1/25 K 63 426/8 LIGHT EMITTING DEVICE, IN PARTICULAR TRAFFIC SIGNAL LIGHT EMITTING DEVICE COMPOSED WITH LIGHT EMITTING DIODES Subject matter of the invention is, according to a first aspect, a light emitting device, in particular a traffic signal light emitting device, composed with light emitting diodes (= LEDs), characterized by (a) a supporting body having a mounting portion for supporting the light emitting device in a socket supplying power to the same, and having a light emitting portion equipped with LEDs; (b) and a circuit board or a sandwich-like circuit board assembly, with the LEDs and the components of a circuit that permits connection of the light emitting device to a mains voltage of at least 110 V without voltage conversion being mounted on said circuit board or said sandwich-like circuit board assembly. Due to the fact that LEDs have a forward voltage in the range of just a few volts, it has been common practice so far - for a desired connection to a mains voltage - to provide for voltage conversion, typically by means of a transformer. In comparison with most circuit components, transformers are bulky and heavy. In addition thereto, it has been usual so far to provide the power supply circuit of an LED assembly in locally separate manner from the LED assembly. Finally, the circuit board carrying a plurality of LEDs usually has been fixed, e.g. by screws, to that apparatus in which the light emitting device is to be of service. As compared with conventional designs, the light emitting device according to the invention distinguishes itself in that it can be manufactured in particularly efficient and inexpensive manner and can be inserted in particularly unprob- 2/25 lematic manner in the apparatus in which it is to be of service. The power supply without voltage conversion leads to a lightweight, small construction with an especially low risk of failure. If, as is preferred, the mounting portion of the supporting body fits into a common screw-type socket or a common plug-in socket or a common bayonet-type socket, as they are commonly employed in particular for incandescent bulbs, the insertion of the light emitting device in the apparatus to be used with the same is particularly simple. In addition thereto, a perfect "conversion solution" has been obtained, i.e. the possibility of replacing without any problem an incandescent bulb used so far for a light emitting device according to the invention. The term "mains voltage" preferably is to be understood as the particular household mains voltage. In many countries, the household mains voltage is 230 V or 110 V. However, the light emitting device according to the invention may also be designed for a mains voltage that is higher than usual household mains voltages, for example when traffic signal installations are operated at a higher mains voltage. The expression "traffic signal light emitting device" is to comprise all light emitting devices through which information is given in traffic. In concrete terms, light emitting devices in traffic lights for road traffic are to be named first, with reference being made in a broader sense also to light signal traffic signs, illuminated signposts, illuminated symbols such as arrow symbols and many more. Traffic signal light emitting devices according to the invention may be employed in particular in road traffic, railroad traffic (e.g. signals along rails), waterborne traffic and airborne traffic (e.g. on airports). Particular reference is also made to the possibility of using the same as runway lighting on airports, where a traffic signal light emitting device in the broadest sense is constituted on the one hand (information to the pilot as to the confines of the runway), but on the other hand also an illumination means. Beyond the sphere of traffic signals mentioned, the light emitting device according to the invention may be employed in particular in the entire field of traffic technology. In excess of this. 3/25 the light emitting device according to the invention may be used in the entire field of illumination. Specific examples to be named here are roadway lighting, garage lighting, building lighting, office lighting, residential lighting. In relation to light emitting devices based on the functional principle of an incandescent bulb, LED light emitting devices distinguish themselves by a much longer lifetime and much lower current consumption. Especially in case of traffic signal light emitting devices, the considerably increased lifetime results in substantial savings in the costs for maintenance and the frequent replacement of incandescent bulbs. Additional subject matter of the invention, according to a second aspect, is a traffic signal light emitting device composed with light emitting diodes {= LEDs), characterized by (a) a supporting body having a mounting portion for supporting the light emitting device in a socket supplying power to the same, and having a light emitting portion equipped with LEDs; (b) and a circuit board or a sandwich-like circuit board assembly having the LEDs mounted thereon; (c) the LEDs, as regards the spacing thereof from the mounting portion of the supporting body, being positioned such that the light emission thereof is largely equivalent to the light reflected by a reflector of an incandescent bulb of a common traffic light. With this second solution according to the invention, the accommodation of the circuit of the power supply on the circuit board or the sandwich-like circuit board assembly no longer is a cogent feature, while however the rule indicated under (c) as to the positioning of the LEDs is a cogent feature. A common traffic light contains, one above the other, a source for green signal light, a source for yellow signal light and a source for red signal light. Usually, these sources are each provided with a white incandescent bulb cooperating with a reflector. The light emitted in forward direction by means of the reflector 4/25 passes to the outside through a colored (green or yellow or red) final pane. The traffic signal light emitting device of the invention, according to the second aspect thereof, is designed such that the LED array thereof provides for light emission equivalent to the embodiment with incandescent bulb and reflector used so far. According to the invention, it has been found that the optimum positioning as regards the spacing from the mounting portion of the supporting body {which is at the same time the optimum positioning with respect to the spacing from the final pane) is of importance, If the LED array is too far away from the the final pane, less than optimum light intensity will be obtained. If the LED array is positioned too close to the final pane, there will be no optimum homogeneity obtained with respect to the light emission for the traffic signal. The features of the light emitting device of the invention, according to the second aspect thereof, may also be realized in the light emitting device according to the first aspect thereof. In the light emitting device according to the invention, the supporting body, except for parts of the mounting portion (especially such parts serving for power supply), preferably consists of plastics material. A plastics supporting body can be manufactured in a large variety of shapes in unproblematic and inexpensive manner. The supporting body often will have the basic shape of a truncated cone, with the mounting portion being located at the smaller-diameter end of the supporting body, and the circuit board or the sandwich-like circuit board assembly being located at the larger-diameter end of the supporting body. Of course, this does not require the exact geometry of a truncated cone; rather, the supporting body constitutes a transition from an end portion of smaller cross-sectional area (= mounting portion) to an end portion of larger cross-sectional area (= light emitting portion with LEDs). In many cases and thus in preferred manner, the supporting body has a configuration of substantially circular cross-section, with the cross-section usually varying when progressing in the longitudinal direction of the supporting body. When the light emitting device according to the invention is intended to be used for a traffic light, the circuit board or the circuit board assembly, in plan view, preferably has a diameter substantially corresponding to the front end diameter of the reflector of a common traffic light. In Germany, for example, the front end diameter of the reflector of a common traffic light is 5/25 200 mm or, for larger traffic lights, 300 mm. With circuit boards or circuit board assemblies having substantially such a size, the light emitting area available is utilized in optimum manner, obtaining optimum homogeneity of the light emission. The supporting body preferably is provided with a translucent end plate in front of the LEDs. The end plate may be provided for protective occlusion e.g. against moisture and dirt. However, the end plate may also be used for optically taking influence on the light emission of the LEDs, e.g. for focussing, for generating substantially parallel beams of light or as scattering disk. The supporting body preferably has an abutment ring for abutment on an abutment portion of an apparatus in which the light emitting device is to be inserted. This provides for additional positional stabilization of the light emitting device in the mounted state thereof, so that supporting in the socket is not the sole feature obtaining positional fixation. The supporting body preferably has a length-adjustable portion by adjustment of which the positioning of the LEDs with respect to the mounting portion of the supporting body can be adjusted. It has already been pointed out further above that it may be advantageous to position the LEDs at a specific location with "respect to the longitudinal direction of the optical axis of the light emitting device (in particular, to position the same such that the light emission of the LEDs is largely equivalent to the light reflected from a reflector of an incandescent bulb of a common traffic light). For being able to easily set a desired advantageous positioning of the LEDs, the afore-mentioned length-adjustable portion is provided. The length-adjustable portion may be realized in particular by a telescope-like portion. Additional subject matter of the invention, according to a third aspect, is a light emitting device, in particular a traffic signal light emitting device, composed with light emitting diodes (= LEDs), characterized in 6/25 (a) that the light emitting device comprises at least one strand containing a multiplicity of LEDs connected in series; (b) that, in each LED strand, there is provided a plurality of Zener diodes connected anti-parallel to at least one LED each; (c) that the LED strand is connected to a mains voltage of at least 110 V without voltage conversion and without pulse modulation; (d) and that the LED strand is connected to the mains voltage via a current limiting means. With this light emitting device according to the invention, the power supply is optimized in terms of manufacturing costs, reliability and space requirements. The multiplicity of the LEDs connected in series in a strand may be of such number that the sum of the forward voltages of these LEDs is close to the mains voltage or a tapped share of the mains voltage; the power loss in other circuit parts can be reduced thereby. By operating the LEDs without pulse modulation, using direct current, the nominal current specified by the producer can be observed by the LEDs. It is thus ensured that the minium lifetime of the LEDs specified by the producer is not impaired by pulse modulation. The Zener voltage of the respective Zener diode may be calculated to be higher than the forward voltage of the LED having the Zener diode connected anti-parallel thereto. In case of interruption of the current flow through the LED, the current flow to the further LEDs of the LED strand is guaranteed. The effect achieved by such a connection is that, e.g. in case of a defective LED, a defective conductive track or a defective solder connection, the LEDs not connected anti-parallel to the Zener diode continue to emit light. When a Zener diode is connected anti-parallel to a plurality of LEDs, which in turn are connected in series, the above calculation can be made based on the sum of the forward voltages of the respective LEDs. Preferably, there are bridged at least two LEDs by a Zener diode, more preferably at least three LEDs and still more preferably at least four LEDs; most preferably, there are bridged three to eight LEDs. 7/25 When it was pointed out hereinbefore that the LED strand is connected to a mains voltage of at least 110 V, this is naturally not supposed to mean that the LED strand is connected directly to mains voltage. As a rule, there are provided intermediate circuit members. The LED strand and the current limiting means may be connected indirectly to the mains voltage of at least 110 V. The intermediate circuit members, e.g. a voltage divider, may have the effect that only part of the mains voltage is applied to the LED strand and the current limiting means. The possibility of being connected in such indirect fashion applies also for the other locations of the present application making use of the term "connected". The current limiting means preferably comprises a resistor. The circuit may be designed such that, at this resistor, there is substantially a voltage drop amounting to the difference between the mains voltage and the voltage across the LED strand. The current limiting means preferably comprises a current impression means. This ensures that the current flowing through the LEDs, and thus the intensity of the LEDs, is largely not affected by fluctuations in mains voltage. In addition thereto, the optimum lifetime of the LEDs is ensured. The current impression means preferably has a resistor and a diode connected in series to the mains voltage, the resistor being connected to the same potential of the mains voltage as the LED strand, and the diode being connected to the opposite potential of the mains voltage. In addition thereto, this current impression means has a transistor, with the base thereof having the potential between the resistor and the diode applied thereto, the collector thereof being connected via the LED strand to the said same potential of the mains voltage, and the emitter thereof being connected, via an additional resistor, to the opposite potential of the mains voltage. The diode may be provided e.g. in the form of a reverse biased Zener diode, a forward biased diode, or a forward biased LED. Thus, a reference voltage independent of the mains voltage is generated. The sum of the base to emitter voltage and the voltage across the additional resistor connected to the emitter, in this type of 8/25 connection, is identical to the voltage across the diode. Due to the fact that the voltage across the additional resistor connected to the emitter in essence is a function of the current through the LED strand, a constant current flow through the LED strand is obtained. The current flowing through the LED strand may be calculated using the following formula: ILED - (UD - UBE)/RE wherein: LED is the current flowing through the LED strand; UD is the current across the diode; UBE is the voltage across the base-to-emitter path of the transistor; RE is the resistance of the additional resistor connected to the emitter. Preferably, the LED strand and the current-limiting circuit are connected to the mains voltage via a rectifying circuit. The rectifying circuit may be realized in particular with a diode or a bridge circuit of diodes. Preferably, there is at least one capacitor connected in parallel to the rectified mains voltage and to the LED strand including a current limiting means. The effect achieved thereby is that the LEDs are operated approximately with direct current. In direct current operation, it is possible to work within the nominal current specified by the producer. The storing function of the capacitor connected in parallel may also be obtained by a series connected inductor. Preferably, the light emitting device is provided with a persistence or afterglow suppressing means. Afterglow of the LEDs may occur due to the charge stored in the afore-mentioned capacitor when said charge flows off via the LEDs after deactivation of the mains voltage. Afterglow causes disturbance especially in case of blinking light emitting devices. An afterglow suppressing means makes sure that, upon deactivation of the mains voltage, the charge stored in said 9/25 capacitor does not flow off via the LEDs. It is thus ensured that no more light is emitted from the light emitting device after deactivation of the mains voltage. The afterglow suppressing means preferably has a forward biased diode, which is located between the rectifying circuit and the afore-mentioned capacitor. The LED strand is connected to the anode of this diode. Located in series with the LED strand, there is provided an electronic switch having at least one control input, with at least one control input of the electronic switch being connected to mains voltage. The diode makes sure that, after deactivation of the mains voltage, current can no longer flow to the control input of the electronic switch and that said control input of the electronic switch is separated from the potential of this capacitor. The electronic switch thus interrupts the current flow through the LED strand. The electronic switch preferably comprises a transistor, the collector thereof being connected via the LED strand to the potential of the anode of the aforementioned diode, the emitter thereof being connected to the mains voltage potential opposite thereto, and the base thereof being connected to the potential of the mains voltage. As there is no longer applied a potential to the base of the transistor after deactivation of the mains voltage, said transistor blocks the current flow through the LEDs. The light emitting device preferably has at least one component provided therein having a function both in the current limiting means and in the afterglow suppressing means. This will be explained in more detail in an embodiment described further below. The light emitting device thus can be designed at lower costs and in more space-saving and reliable manner Preferably, the capacitor has at least one resistor connected in parallel thereto. The resistor discharges the capacitor upon deactivation of the mains voltage, thereby preventing afterglow of the LEDs. Preferably, there is at least one diode connected between the capacitor and the input of the current limiting means. The diode makes sure that, after deactivation of the mains voltage, current can no longer flow to the control input of the current limiting means and that the 10/25 control input of the current limiting means is separated from the potential of the capacitor. This, too, prevents afterglow of the LEDs. The LEDs of the LED strand preferably have at least one capacitor connected in parallel thereto, with each capacitor having at least one LED connected in parallel thereto. It is thus possible to prevent damage to the LEDs by possible voltage peaks. There are embodiments possible in which each LED has a capacitor connected in parallel thereto, or also embodiments in which groups of LEDs or even all LEDs have a capacitor connected in parallel thereto. The arrangement of the LEDs and the power supply of the LEDs are preferably redundant starting from the mains or power input. Even in case of any failure at an arbitrary location of the LEDs or the power supply of the LEDs, there is still possible a function of the tight-emitting device with reduced light emission. Due to the very simple construction of the power supply according to the invention, the redundant design can be realized without substantial extra costs and without substantial additional space required. It is emphasized that it is possible in an alternative preferred development of the invention to provide for redundancy of only part of the LED assembly and the power supply, i.e. so to speak to begin with the redundant design somewhat remote from the mains input. The LEDs and the power supply of the LEDs preferably are mounted on a circuit board or a sandwich-like circuit board assembly. Flexible circuit boards are conceivable as well. The LEDs of the redundant LED strands preferably are arranged on the circuit board or the sandwich-like circuit board assembly such that a substantially homogeneous emission of light is obtained in case of failure of a redundant part. In particular, the LEDs of the redundant strands may be arranged in substantially alternating manner. The LEDs of the redundant LED strands preferably are arranged on the circuit board or the sandwich-like circuit board assembly such that, in case of failure of a redundant part, such non-homogeneous emission of light arises that the 11/25 failure becomes recognizable to an observer. For example, it is possible to arrange a first group of LEDs on a first portion of the light emitting area and a redundant, second group of LEDs on a second portion of the light emitting area, e.g. in the form of two halves of a circle. Each of the two groups may be subdivided further, so as to form e.g. four sectors of a circle or four strips within a square. Additional subject matter of the invention resides, according to a fourth aspect, in a light emitting device, in particular a traffic signal light emitting device, composed with light emitting diodes (= LEDs), characterized in (a) that the LEDs are connected to a mains voltage of at least 110 V; (b) and that the assembly of the LEDs and the power supply of the LEDs are redundant starting from the mains input. It has already been mentioned hereinbefore that the redundant design guarantees the function of the light emitting device in case of any electric failure, though with reduced light emission. This is of particularly great importance especially also with traffic signal light emitting devices. With a corresponding design, as mentioned hereinbefore as preferred embodiment, a traffic signal light emitting device according to the invention may be used instead of an incandescent bulb by simple replacement thereof. The design preferably is such that the reflector of a common traffic light remains in the traffic light. The colored end pane provided may be left in the traffic light as well. Traffic signal light emitting devices according to the invention preferably are provided with colored LEDs, e.g. red LEDs for a red traffic light segment, green LEDs for a green traffic light segment and yellow LEDs for a yellow traffic light segment. On the other hand, it is also possible with the invention to make use of white LEDs, not only for traffic signal light emitting devices, but especially for lighting systems. 12/25 The invention preferably does not make use of a pulse circuit in order to operate the LEDs with mains voltage. It is emphasized that numerous features of the invention may also be realized with a light emitting device that is not designed for connection to a mains voltage of at least 110 V, but e.g. for a proprietary voltage below 110 V, preferably in the range from 24 to 110 V. 13/25 The invention and preferred embodiments of the invention will be explained in more detail hereinafter by way of embodiments shown in theaccompanying/drrawings in wnich Fig. 1 shows a traffic signal light emitting device, in a side view and partly in a longitudinal sectional view; Fig. 2 shows part of a traffic signal light emitting device of alternative design, in a longitudinal sectional view; Fig. 3 shows part of a traffic signal light emitting device of alternative design, in a partial longitudinal sectional view; Fig. 4 shows a circuit diagram for the LEDs and the current limiting means for the LEDs in a light emitting device; Fig. 5 shows a circuit diagram for the LEDs and the current limiting means for the LEDs in a light emitting device, with the current limiting means being realized in the form of a current impression means. Fig. 1 illustrates, in a longitudinal sectional view containing the optical axis 2, part of a traffic light segment (either a green traffic light segment or a yellow traffic light segment or a red traffic light segment), viz. a front portion of a reflector 4 and a forward, colored end pane 6. In the cut-away rear portion of the reflector 4, the reflector 4 carries a screw-type socket in which an incandescent bulb is threadedly mounted in a common traffic light segment. The reflector 4 has its front end portion attached to a housing of the respective traffic light segment, as indicated in Fig. 1 by way of a front end flange 8 of reflector 4 and axes 10 of mounting screws. the incandescent bulb usually present in a traffic light segment operated with an incandescent bulb has been threadedly removed, and instead of the latter a traffic signal light emitting device 20 as illustrated has been threadedly mounted in the same socket. In the front end portion thereof (at the top in Fig. 1), the light emitting device 20 becomes larger in size so as to correspond almost to the 14/25 inner diameter of the reflector 4 at the front end portion thereof. At that location, the light emitting device 20 has a rubber ring 22 attached thereto, which is supported in a circumferential groove of the light emitting device 20. The outer diameter of the ring 22 and the axial positioning of the same (optical axis 2 = longitudinal central axis of light emitting device 20) are matched such that, when the light emitting device 20 is completely threadedly engaged in the screw-type socket (not shown), the ring 22 has a rear end portion of its outer circumference abutting the inside of the reflector 4, thereby providing for additional stabilization of the light emitting device. Via the screw-type socket, not shown, the light emitting device 20 is connected to a mains voltage of e.g. 110 V or 230 V in the same manner as an incandescent bulb, In the front end portion {at the top in Fig. 1), the light emitting device 20 carries a circuit board 24 extending at right angles with respect to the axis 2. The circuit board 24 has an outer diameter only slightly smaller than that of the largest inner diameter of the reflector 4. On the front side of the circuit board 24, there is mounted a multiplicity of LEDs 30. The rear side of the circuit board 24 has circuit components 32 mounted thereon. An embodiment of an LED assembly and a circuit will still be described further below. In this place, it is merely pointed out that the circuit permits operation of the LEDs 30 with the mains voltage, without voltage conversion and without pulse modulation. The traffic signal light emitting device 20 illustrated and described thus is composed of a - roughly speaking - mushroom-shaped supporting body 34 and the afore-mentioned circuit board 24 along with the LEDs 30 and circuit components 32 mounted thereto. The supporting body 34 preferably is made of plastics material and is manufactured preferably by injection molding. The rear end portion of the supporting body 34 having the screw-type thread constitutes a mounting portion for mounting the light emitting device; the front end portion of the supporting body 34, supporting the circuit board 24, constitutes a light emitting portion of the light emitting device 20. The broken line illustrates a translucent end plate 36 of the light emitting device 20, which may be provided optionally. 15/25 Fig. 2 illustrates an alternative in which a front circuit board 24a and a rear circuit board 24b are provided instead of circuit board 24. The circuit boards 24a and 24b constitute a sandwich-like circuit board assembly 38. The front circuit board 24a carries the LEDs 30 and components 32a which, in terms of circuit technology, are to be positioned most expediently closely adjacent to the LEDs 30 (in particular Zener diodes and capacitors, cf. the description further below). The rear circuit board 24b carries the remaining components 32b. The circuit boards 24a and 24b are electrically connected to each other via plug connectors 40. Fig. 3 illustrates a length-adjustable portion 42 of a supporting body of a light emitting device 20. A cylindrical rear portion 44 of the supporting body projects into a front portion 46 of the supporting body of somewhat larger diameter, in the fashion of a telescope-type connection. The rear portion 44 has a radially outwardly projecting pin 48 attached thereto. This pin 48 cooperates with a groove or a slot 50 which, in the cylindrical front portion 46, is provided along a spiral path, analogous to a thread. Upon rotation of the portions 44 and 46 relative to each other, the effective length of the supporting body, as measured in the direction of the axis 2, changes. The fit between the front portion 46 and the rear portion 44 is so tight that a once set longitudinal adjustment does not change by itself. Optionally, there may be provided a friction-enhancing intermediate ring between the portions 46 and 44. The length-adjustable portion 42 is located in that part of the supporting body that is referenced 52 in Fig. 1. Fig. 4 schematically illustrates a circuit arrangement according to an embodiment of the invention. Block 114 shows a circuit unit of an embodiment of the light emitting device according to the invention, consisting of power or mains input 103, rectifier 108, current-limiting circuit 106, diode D, LED strand 102, capacitor C1, capacitor CN+1,and resistor R4. 16/25 The rectifying circuit 108 serves to convert an alternating voltage possibly applied to the mains input into a direct voltage, which consequently is applied between points 118 and 110. Without excluding other embodiments, the present embodiment makes use of a bridge-type rectifier. Block 102 has LEDs (LED 1 to LED N) connected in series, with Zener diodes (ZD 1 to ZD N) being connected in anti-parallel fashion and capacitors (C 2 to C N) being provided in parallel. Without excluding other embodiments, the present embodiment has for each LED (LED 1 to LED N) one capacitor (capacitor C2 to C N) connected in parallel thereto and for each group of four LEDs (LED 1 to LED N) one Zener diode connected anti-parallel thereto. In the present embodiment, the forward voltage of the LEDs (LED 1 to LED N) is approx. 3.5 volts each, with 31 diodes being arranged in series. The breakthrough voltage of the Zener diode (ZD 1 to ZD N) is higher than the sum of the forward voltages of the respective light emitting diodes (LED 1 to LED N) bridged in anti-parallel manner. This ensures the current flow across the Zener diode (ZD 1 to ZD N) in case a failure arises in the light emitting diodes (LED 1 to LED N) bridged in anti-parallel manner, the supply lines to the same or the solder connections thereof. Depending on the wavelength, the LEDs typically have a forward voltage of 2 to 4 V and are selected e.g. with a nominal current of 50 mA. The maximum admissible power loss of the Zener diodes has to be at least as large as the product of Zener voltage and nominal current through the LEDs. Diode D, in forward direction, is located between the rectifier circuit 108, i,e. potential 108, and the LED strand 102, i.e. potential 104. Block 106 illustrates the current-limiting circuit of an embodiment of the light emitting device. It is realized by an npn transistor and the resistors Rl, R2 and R3. The resistors R1 and R2 are connected in series between the potentials 118 and 110. The transistor T1 has its base connected to the potential between the resistors R1 and R2. The emitter of transistor T1 is connected to the potential 110. The collector of transistor T1 is connected to the potential 104 via the 17/25 resistor R3 and the LED strand 102 connected in series therewith and including the LEDs LED1 to LEDN. The base voltage is set via the resistors R1 and R2, thereby determining the collector current on the basis of the characteristics of the transistor. In the present embodiment, the resistor R1 is set to a value of approx. 100 kiloohms, resistor R2 is set to a value of approx. 10 kiloohms, and resistor R3 is set to a value of approx. 100 ohms. The transistor used is of the type MPSA 42. The current-limiting circuit may be composed, for example, of a MOSFET transistor as well. In both cases described, the current limitation is obtained by means of the resistor R3. The transistor has the function of an electronic switch. The circuit described may be composed in equivalent manner by means of a pnp bipolar transistor. !n that case, the emitter thereof has the potential (104) of the anode of diode (D) connected thereto, the collector thereof is connected to the opposite mains voltage potential via the LED strand (102), and the base thereof is connected to the potential of the mains voltage. The capacitor C1 is connected in parallel to the LED strand 102 between the potentials 104 and 110. The capacitor C1 serves to smooth the half-waves of the rectified alternating voltage, so that the LEDs have a quasi continuous direct voltage supplied thereto. The capacitor CN + 1 is connected in parallel to the LED strand 102 between the potentials 118 and 110. When the circuit is connected to mains voltage, capacitor CN+1 makes sure that the voltage divider 12 at the base of transistor T1 approximately has the peak voltage supplied thereto between the peaks of the half-waves. It is thus ensured that the transistor T1 connects through between the peaks of the half-waves and that the LEDs may emit light as these also have current supplied thereto via capacitor C1. For preventing persistence or afterglow upon deactivation of the mains voltage 103, the present embodiment provides a discharge resistor R4 connected in parallel to capacitor C1, and the diode D separates the voltage divider of the 18/25 base of transistor T1 from the potential 104 of capacitor C1, whereupon the transistor blocks the current flow through the diodes. Provided upstream of the rectifier at the mains input, there may be an optional voltage divider circuit permitting the light emitting unit to be easily reconfigured for different mains voltages. The circuit depicted in block 116 corresponds exactly to the above-described circuit in block 14 and is of redundant construction to the above-described circuit starting from the mains input. The circuit illustrated in Fig. 5 differs from the circuit illustrated in Fig. 4 merely in the following respect: Instead of resistor R2, there is provided a diode Dref. Resistor R3 has been omitted. A resistor R13 and a capacitor CD are newly provided. The capacitor CD is connected in parallel to the diode Dref. The embodiment according to Fig. 5 has a current impression means. The control is realized by way of resistor R1 and the forward biased diode Dref. Located in series with the LED strand are the collector-to-emitter path of the npn bipolar transistor T1 and the resistor R13. The base voltage of the transistor T1 is tapped by diode Dref. The sum of the voltage drop across R13 and of the voltage drop across the base-to-emitter path of T1 corresponds to the voltage across the diode Dref. As the voltage drop across the diode Dref is independent of the mains voltage to the largest possible extent, the current flowing through resistor R13 thus is independent of the same, so that the current flowing through the LEDs is independent of the mains voltage to the largest possible extent as well. The resistor R13 should be dimensioned such that the quotient of the voltage across the diode Dref minus the voltage across the base-to-emitter path, divided by the resistance of resistor R13, yields substantially the nominal current of the LEDs. An npn bipolar transistor T1 is to be chosen such that the mains voltage may be present across the collector-to-emitter path and such that the current set can flow through the LEDs across the collector- 19/25 to-emitter path. The diode Dref can be realized by a forward biased LED or a forward biased diode or a reverse biased Zener diode. Transistor T1 may also be realized by a field effect transistor. For generating a constant current, a constant current diode may be used as well. The diode Dref and the resistor R1 may also be replaced by a reference voltage source. In the circuit described, the transistor has a function in the current impression means and in the afterglow suppressing means. The circuit described may be composed in equivalent manner by means of a pnp bipolar transistor. 20 WE CLAIM : 1. A light emitting device, in particular a traffic signal light emitting device, composed with light emitting diodes (=LEDs) (30), comprising the following features : (a) the light emitting device comprises at least one strand (102) having a multiplicity of LEDs (30) connected in series; (b) the LED strand (102) is adapted to be connected substantially to a mains voltage (103) of at least 110V without voltage conversion and without pulse modulation; (c) the LED strand is adapted to be connected to the mains voltage via a current limiting means (106); and (d) there is provided a means for suppressing afterglow (R4, D, Tl) of the LEDs (30). 2. A light emitting device as claimed in claim 1, wherein LED strand (102) has a plurality of Zener diodes (ZD) provided therein, each being connected in parallel to at least one LED (30) and being reverse biased. 3. A light emitting device as claimed in claim 1 or 2, wherein the LED strand and the current limiting means (106) are adapted to be connected to the mains voltage (103) via a rectifying circuit (108). 4. A light emitting device as claimed in any of claims 1 to 3, wherein the assembly of the LEDS (30) and the power supply of the LEDs (30) are redundant starting from the mains input. 21 5. A light emitting device as claimed in any of claims 1 to 4, wherein (a) a supporting body (34) having a mounting portion for supporting the light emitting device (30) in a socket supplying power to the same, and having a light emitting, portion equipped with LEDs (30); (b) and a circuit board (24) or a sandwich - like circuit board assembly (24a, 24b), with the LEDs (30) and the components (32) of a circuit that permits connection of the light emitting device (20) to a mains voltage of at least 110V without voltage conversion being mounted on said circuit board (24) or said sandwich-like circuit board assembly (24a, 24b). 6. A light emitting device as claimed in claim 5, wherein the LEDs (30), in terms of the spacing thereof from the mounting portion of the supporting body (34), are positioned such that the light emission thereof is largely equivalent to the light reflected by a reflector (4) of a common traffic light. 7. A light emitting device as claimed in claims 5 or 6, wherein the supporting body (34), except for parts of the mounting portion, consists of plastics material. 8. A light emitting device as claimed in any of claims 5 to 7, wherein the supporting body (34) has a configuration of substantially circular cross-sectional area. 9. A light emitting device as claimed in any of claims 5 to 8, wherein the circuit board assembly (24a, 24b), as seen in plan view, has a diameter which substantially corresponds to the front end diameter of the reflector (4) of a common traffic light. 22 10. A light emitting device as claimed in any of claims 5 to 9, wherein the mounting portion fits into a common screw - type socket provided for a particular incandescent bulb, or into a common plug- in socket or a common bayonet-type socket. 11. A light emitting device as claimed in any of claims 5 to 10, wherein the supporting body is provided with a translucent end plate (36) in front of the LEDs (30). 12. A light emitting device as claimed in any of claims 5 to 11, wherein the supporting body (34) comprises an abutment ring (22) for abutment on an abutment portion of an apparatus in which the light emitting device (20) is to be inserted. 13. A light emitting device as claimed in any of claims 5 to 12, wherein the supporting body (34) has a length-adjustable portion (42) by adjustment of which the positioning of the LEDs (30) with respect to the mounting portion of the supporting body (34) can be adjusted. 14. A light emitting device as claimed in any of claims 1 to 13, wherein the current limiting means (106) comprises a resistor (R3). 15. A light emitting device as claimed in any of claims 1 to 14, wherein the current limiting means (106) comprises a current impression means. 16. A light emitting device as claimed in claim 15, wherein the current impression means (106) comprises a resistor (Rl) and a diode (Dref) that are connected in series to the mains voltage (103), 23 the resistor (Rl) being connected to the same potential (118) of the mains voltage (103) as the LED strand (102), and the diode (Dref) being connected to the opposite potential (110) of the mains voltage (103), and comprises furthermore a transistor (Tl), with the base thereof having the potential between the resistor (Rl) and the diode (Dref) applied thereto, the collector thereof being connected via the LED strand (102) to the said same potential (118) of the mains voltage (103), and the emitter thereof being connected, via an additional resistor (R13), to the opposite potential (110) of the mains voltage (103). 17. A light emitting device as claimed in any of claims 1 to 16, wherein there is at least one capacitor (Cl) connected in parallel to the LED strand (102) comprising the current limiting means (106). 18. A light emitting device as claimed in claim 17, wherein a forward biased diode (D) is located between the rectifying circuit (108) and the capacitor (Cl), and in that an electronic switch (Tl) having at least one control input is provided in series with the LED strand (102) connected to the anode of the diode (D), said at least one control input of the electronic switch (Tl) being connected to the mains voltage (103). 19. A light emitting device as claimed in claim 18, wherein the electronic switch is constituted by a transistor (Tl), the collector thereof being connected via the LED strand (102) to the potential (104) of the anode of the diode (D), the emitter thereof being connected to the mains voltage potential (110) opposite thereto, and the base thereof being connected to the potential (118) of the mains voltage. 24 20. A light emitting device as claimed in any of claims 1 to 19, wherein there is provided at least one component (Tl) having a function both in the current limiting means (106) and in the means for suppressing afterglow (R4, D, Tl) of the LEDs (30). 21. A light emitting device as claimed in any of claims 17 to 20, wherein the capacitor (Cl) has at least one resistor (R4) connected in parallel thereto. 22. A light emitting device as claimed in any of claims 1 to 21, wherein the LEDs (30) of the LED strand (102) have at least one capacitor (C2 to CN) connected in parallel thereto, with each capacitor (C2 to CN) being connected in parallel to at least one LED (30). 23. A light emitting device as claimed in any of claims 4 to 22, wherein the LEDs (30) of the redundant LED strands (102) are mounted on the circuit board (24) or the sandwich-like circuit board assembly (24a, 24b) such that a substantially homogeneous emission of light is obtained in case of failure of a redundant part (104, 116). 24. A light emitting device as claimed in any of claims 4 to 22, wherein the LEDs (30) of the redundant LED strands (102) are arranged on the circuit board (24) or the sandwich-like circuit board assembly (24a, 24b) such that, in case of failure of a redundant part (114, 116), such non- homogeneous emission of light arises that the failure becomes recognizable to an observer. There is disclosed a light emitting device, in particular a traffic signal light emitting device, composed with light emitting diodes (=LEDs) (30), said device having at least one strand (102) with a multiplicity of LEDs (30) connected in series; said strand being adapted to be connected via a current limiting means, substantially to a mains voltage of at least 110V without voltage conversion and without pulse modulation; and having a means for suppressing afterglow of the LEDs (30).

Full Text

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K 63 426/8
LIGHT EMITTING DEVICE, IN PARTICULAR TRAFFIC SIGNAL LIGHT EMITTING DEVICE COMPOSED WITH LIGHT EMITTING DIODES
Subject matter of the invention is, according to a first aspect, a light emitting device, in particular a traffic signal light emitting device, composed with light emitting diodes (= LEDs), characterized by
(a) a supporting body having a mounting portion for supporting the light
emitting device in a socket supplying power to the same, and having a
light emitting portion equipped with LEDs;
(b) and a circuit board or a sandwich-like circuit board assembly, with the
LEDs and the components of a circuit that permits connection of the light
emitting device to a mains voltage of at least 110 V without voltage
conversion being mounted on said circuit board or said sandwich-like
circuit board assembly.
Due to the fact that LEDs have a forward voltage in the range of just a few volts, it has been common practice so far - for a desired connection to a mains voltage - to provide for voltage conversion, typically by means of a transformer. In comparison with most circuit components, transformers are bulky and heavy. In addition thereto, it has been usual so far to provide the power supply circuit of an LED assembly in locally separate manner from the LED assembly. Finally, the circuit board carrying a plurality of LEDs usually has been fixed, e.g. by screws, to that apparatus in which the light emitting device is to be of service.
As compared with conventional designs, the light emitting device according to the invention distinguishes itself in that it can be manufactured in particularly efficient and inexpensive manner and can be inserted in particularly unprob-

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lematic manner in the apparatus in which it is to be of service. The power supply without voltage conversion leads to a lightweight, small construction with an especially low risk of failure.
If, as is preferred, the mounting portion of the supporting body fits into a common screw-type socket or a common plug-in socket or a common bayonet-type socket, as they are commonly employed in particular for incandescent bulbs, the insertion of the light emitting device in the apparatus to be used with the same is particularly simple. In addition thereto, a perfect "conversion solution" has been obtained, i.e. the possibility of replacing without any problem an incandescent bulb used so far for a light emitting device according to the invention.
The term "mains voltage" preferably is to be understood as the particular household mains voltage. In many countries, the household mains voltage is 230 V or 110 V. However, the light emitting device according to the invention may also be designed for a mains voltage that is higher than usual household mains voltages, for example when traffic signal installations are operated at a higher mains voltage.
The expression "traffic signal light emitting device" is to comprise all light emitting devices through which information is given in traffic. In concrete terms, light emitting devices in traffic lights for road traffic are to be named first, with reference being made in a broader sense also to light signal traffic signs, illuminated signposts, illuminated symbols such as arrow symbols and many more. Traffic signal light emitting devices according to the invention may be employed in particular in road traffic, railroad traffic (e.g. signals along rails), waterborne traffic and airborne traffic (e.g. on airports). Particular reference is also made to the possibility of using the same as runway lighting on airports, where a traffic signal light emitting device in the broadest sense is constituted on the one hand (information to the pilot as to the confines of the runway), but on the other hand also an illumination means. Beyond the sphere of traffic signals mentioned, the light emitting device according to the invention may be employed in particular in the entire field of traffic technology. In excess of this.

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the light emitting device according to the invention may be used in the entire field of illumination. Specific examples to be named here are roadway lighting, garage lighting, building lighting, office lighting, residential lighting.
In relation to light emitting devices based on the functional principle of an incandescent bulb, LED light emitting devices distinguish themselves by a much longer lifetime and much lower current consumption. Especially in case of traffic signal light emitting devices, the considerably increased lifetime results in substantial savings in the costs for maintenance and the frequent replacement of incandescent bulbs.
Additional subject matter of the invention, according to a second aspect, is a traffic signal light emitting device composed with light emitting diodes {= LEDs), characterized by
(a) a supporting body having a mounting portion for supporting the light
emitting device in a socket supplying power to the same, and having a
light emitting portion equipped with LEDs;
(b) and a circuit board or a sandwich-like circuit board assembly having the
LEDs mounted thereon;
(c) the LEDs, as regards the spacing thereof from the mounting portion of the
supporting body, being positioned such that the light emission thereof is
largely equivalent to the light reflected by a reflector of an incandescent
bulb of a common traffic light.
With this second solution according to the invention, the accommodation of the circuit of the power supply on the circuit board or the sandwich-like circuit board assembly no longer is a cogent feature, while however the rule indicated under (c) as to the positioning of the LEDs is a cogent feature.
A common traffic light contains, one above the other, a source for green signal light, a source for yellow signal light and a source for red signal light. Usually, these sources are each provided with a white incandescent bulb cooperating with a reflector. The light emitted in forward direction by means of the reflector

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passes to the outside through a colored (green or yellow or red) final pane. The traffic signal light emitting device of the invention, according to the second aspect thereof, is designed such that the LED array thereof provides for light emission equivalent to the embodiment with incandescent bulb and reflector used so far. According to the invention, it has been found that the optimum positioning as regards the spacing from the mounting portion of the supporting body {which is at the same time the optimum positioning with respect to the spacing from the final pane) is of importance, If the LED array is too far away from the the final pane, less than optimum light intensity will be obtained. If the LED array is positioned too close to the final pane, there will be no optimum homogeneity obtained with respect to the light emission for the traffic signal.
The features of the light emitting device of the invention, according to the second aspect thereof, may also be realized in the light emitting device according to the first aspect thereof. In the light emitting device according to the invention, the supporting body, except for parts of the mounting portion (especially such parts serving for power supply), preferably consists of plastics material. A plastics supporting body can be manufactured in a large variety of shapes in unproblematic and inexpensive manner. The supporting body often will have the basic shape of a truncated cone, with the mounting portion being located at the smaller-diameter end of the supporting body, and the circuit board or the sandwich-like circuit board assembly being located at the larger-diameter end of the supporting body. Of course, this does not require the exact geometry of a truncated cone; rather, the supporting body constitutes a transition from an end portion of smaller cross-sectional area (= mounting portion) to an end portion of larger cross-sectional area (= light emitting portion with LEDs). In many cases and thus in preferred manner, the supporting body has a configuration of substantially circular cross-section, with the cross-section usually varying when progressing in the longitudinal direction of the supporting body. When the light emitting device according to the invention is intended to be used for a traffic light, the circuit board or the circuit board assembly, in plan view, preferably has a diameter substantially corresponding to the front end diameter of the reflector of a common traffic light. In Germany, for example, the front end diameter of the reflector of a common traffic light is

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200 mm or, for larger traffic lights, 300 mm. With circuit boards or circuit board assemblies having substantially such a size, the light emitting area available is utilized in optimum manner, obtaining optimum homogeneity of the light emission.
The supporting body preferably is provided with a translucent end plate in front of the LEDs. The end plate may be provided for protective occlusion e.g. against moisture and dirt. However, the end plate may also be used for optically taking influence on the light emission of the LEDs, e.g. for focussing, for generating substantially parallel beams of light or as scattering disk.
The supporting body preferably has an abutment ring for abutment on an abutment portion of an apparatus in which the light emitting device is to be inserted. This provides for additional positional stabilization of the light emitting device in the mounted state thereof, so that supporting in the socket is not the sole feature obtaining positional fixation.
The supporting body preferably has a length-adjustable portion by adjustment of which the positioning of the LEDs with respect to the mounting portion of the supporting body can be adjusted. It has already been pointed out further above that it may be advantageous to position the LEDs at a specific location with "respect to the longitudinal direction of the optical axis of the light emitting device (in particular, to position the same such that the light emission of the LEDs is largely equivalent to the light reflected from a reflector of an incandescent bulb of a common traffic light). For being able to easily set a desired advantageous positioning of the LEDs, the afore-mentioned length-adjustable portion is provided. The length-adjustable portion may be realized in particular by a telescope-like portion.
Additional subject matter of the invention, according to a third aspect, is a light emitting device, in particular a traffic signal light emitting device, composed with light emitting diodes (= LEDs), characterized in

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(a) that the light emitting device comprises at least one strand containing a
multiplicity of LEDs connected in series;
(b) that, in each LED strand, there is provided a plurality of Zener diodes
connected anti-parallel to at least one LED each;
(c) that the LED strand is connected to a mains voltage of at least 110 V
without voltage conversion and without pulse modulation;
(d) and that the LED strand is connected to the mains voltage via a current
limiting means.
With this light emitting device according to the invention, the power supply is optimized in terms of manufacturing costs, reliability and space requirements.
The multiplicity of the LEDs connected in series in a strand may be of such number that the sum of the forward voltages of these LEDs is close to the mains voltage or a tapped share of the mains voltage; the power loss in other circuit parts can be reduced thereby. By operating the LEDs without pulse modulation, using direct current, the nominal current specified by the producer can be observed by the LEDs. It is thus ensured that the minium lifetime of the LEDs specified by the producer is not impaired by pulse modulation.
The Zener voltage of the respective Zener diode may be calculated to be higher than the forward voltage of the LED having the Zener diode connected anti-parallel thereto. In case of interruption of the current flow through the LED, the current flow to the further LEDs of the LED strand is guaranteed. The effect achieved by such a connection is that, e.g. in case of a defective LED, a defective conductive track or a defective solder connection, the LEDs not connected anti-parallel to the Zener diode continue to emit light. When a Zener diode is connected anti-parallel to a plurality of LEDs, which in turn are connected in series, the above calculation can be made based on the sum of the forward voltages of the respective LEDs. Preferably, there are bridged at least two LEDs by a Zener diode, more preferably at least three LEDs and still more preferably at least four LEDs; most preferably, there are bridged three to eight LEDs.

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When it was pointed out hereinbefore that the LED strand is connected to a mains voltage of at least 110 V, this is naturally not supposed to mean that the LED strand is connected directly to mains voltage. As a rule, there are provided intermediate circuit members. The LED strand and the current limiting means may be connected indirectly to the mains voltage of at least 110 V. The intermediate circuit members, e.g. a voltage divider, may have the effect that only part of the mains voltage is applied to the LED strand and the current limiting means. The possibility of being connected in such indirect fashion applies also for the other locations of the present application making use of the term "connected".
The current limiting means preferably comprises a resistor. The circuit may be designed such that, at this resistor, there is substantially a voltage drop amounting to the difference between the mains voltage and the voltage across the LED strand.
The current limiting means preferably comprises a current impression means. This ensures that the current flowing through the LEDs, and thus the intensity of the LEDs, is largely not affected by fluctuations in mains voltage. In addition thereto, the optimum lifetime of the LEDs is ensured.
The current impression means preferably has a resistor and a diode connected in series to the mains voltage, the resistor being connected to the same potential of the mains voltage as the LED strand, and the diode being connected to the opposite potential of the mains voltage. In addition thereto, this current impression means has a transistor, with the base thereof having the potential between the resistor and the diode applied thereto, the collector thereof being connected via the LED strand to the said same potential of the mains voltage, and the emitter thereof being connected, via an additional resistor, to the opposite potential of the mains voltage. The diode may be provided e.g. in the form of a reverse biased Zener diode, a forward biased diode, or a forward biased LED. Thus, a reference voltage independent of the mains voltage is generated. The sum of the base to emitter voltage and the voltage across the additional resistor connected to the emitter, in this type of

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connection, is identical to the voltage across the diode. Due to the fact that the voltage across the additional resistor connected to the emitter in essence is a function of the current through the LED strand, a constant current flow through the LED strand is obtained.
The current flowing through the LED strand may be calculated using the following formula:
ILED - (UD - UBE)/RE
wherein:
LED is the current flowing through the LED strand;
UD is the current across the diode;
UBE is the voltage across the base-to-emitter path of the transistor;
RE is the resistance of the additional resistor connected to the emitter.
Preferably, the LED strand and the current-limiting circuit are connected to the mains voltage via a rectifying circuit. The rectifying circuit may be realized in particular with a diode or a bridge circuit of diodes.
Preferably, there is at least one capacitor connected in parallel to the rectified mains voltage and to the LED strand including a current limiting means. The effect achieved thereby is that the LEDs are operated approximately with direct current. In direct current operation, it is possible to work within the nominal current specified by the producer. The storing function of the capacitor connected in parallel may also be obtained by a series connected inductor.
Preferably, the light emitting device is provided with a persistence or afterglow suppressing means. Afterglow of the LEDs may occur due to the charge stored in the afore-mentioned capacitor when said charge flows off via the LEDs after deactivation of the mains voltage. Afterglow causes disturbance especially in case of blinking light emitting devices. An afterglow suppressing means makes sure that, upon deactivation of the mains voltage, the charge stored in said

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capacitor does not flow off via the LEDs. It is thus ensured that no more light is emitted from the light emitting device after deactivation of the mains voltage.
The afterglow suppressing means preferably has a forward biased diode, which is located between the rectifying circuit and the afore-mentioned capacitor. The LED strand is connected to the anode of this diode. Located in series with the LED strand, there is provided an electronic switch having at least one control input, with at least one control input of the electronic switch being connected to mains voltage. The diode makes sure that, after deactivation of the mains voltage, current can no longer flow to the control input of the electronic switch and that said control input of the electronic switch is separated from the potential of this capacitor. The electronic switch thus interrupts the current flow through the LED strand.
The electronic switch preferably comprises a transistor, the collector thereof being connected via the LED strand to the potential of the anode of the aforementioned diode, the emitter thereof being connected to the mains voltage potential opposite thereto, and the base thereof being connected to the potential of the mains voltage. As there is no longer applied a potential to the base of the transistor after deactivation of the mains voltage, said transistor blocks the current flow through the LEDs.
The light emitting device preferably has at least one component provided therein having a function both in the current limiting means and in the afterglow suppressing means. This will be explained in more detail in an embodiment described further below. The light emitting device thus can be designed at lower costs and in more space-saving and reliable manner
Preferably, the capacitor has at least one resistor connected in parallel thereto. The resistor discharges the capacitor upon deactivation of the mains voltage, thereby preventing afterglow of the LEDs. Preferably, there is at least one diode connected between the capacitor and the input of the current limiting means. The diode makes sure that, after deactivation of the mains voltage, current can no longer flow to the control input of the current limiting means and that the

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control input of the current limiting means is separated from the potential of the capacitor. This, too, prevents afterglow of the LEDs.
The LEDs of the LED strand preferably have at least one capacitor connected in parallel thereto, with each capacitor having at least one LED connected in parallel thereto. It is thus possible to prevent damage to the LEDs by possible voltage peaks. There are embodiments possible in which each LED has a capacitor connected in parallel thereto, or also embodiments in which groups of LEDs or even all LEDs have a capacitor connected in parallel thereto.
The arrangement of the LEDs and the power supply of the LEDs are preferably redundant starting from the mains or power input. Even in case of any failure at an arbitrary location of the LEDs or the power supply of the LEDs, there is still possible a function of the tight-emitting device with reduced light emission. Due to the very simple construction of the power supply according to the invention, the redundant design can be realized without substantial extra costs and without substantial additional space required. It is emphasized that it is possible in an alternative preferred development of the invention to provide for redundancy of only part of the LED assembly and the power supply, i.e. so to speak to begin with the redundant design somewhat remote from the mains input.
The LEDs and the power supply of the LEDs preferably are mounted on a circuit board or a sandwich-like circuit board assembly. Flexible circuit boards are conceivable as well.
The LEDs of the redundant LED strands preferably are arranged on the circuit board or the sandwich-like circuit board assembly such that a substantially homogeneous emission of light is obtained in case of failure of a redundant part. In particular, the LEDs of the redundant strands may be arranged in substantially alternating manner.
The LEDs of the redundant LED strands preferably are arranged on the circuit board or the sandwich-like circuit board assembly such that, in case of failure of a redundant part, such non-homogeneous emission of light arises that the

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failure becomes recognizable to an observer. For example, it is possible to arrange a first group of LEDs on a first portion of the light emitting area and a redundant, second group of LEDs on a second portion of the light emitting area, e.g. in the form of two halves of a circle. Each of the two groups may be subdivided further, so as to form e.g. four sectors of a circle or four strips within a square.
Additional subject matter of the invention resides, according to a fourth aspect, in a light emitting device, in particular a traffic signal light emitting device, composed with light emitting diodes (= LEDs), characterized in
(a) that the LEDs are connected to a mains voltage of at least 110 V;
(b) and that the assembly of the LEDs and the power supply of the LEDs are
redundant starting from the mains input.
It has already been mentioned hereinbefore that the redundant design guarantees the function of the light emitting device in case of any electric failure, though with reduced light emission. This is of particularly great importance especially also with traffic signal light emitting devices.
With a corresponding design, as mentioned hereinbefore as preferred embodiment, a traffic signal light emitting device according to the invention may be used instead of an incandescent bulb by simple replacement thereof. The design preferably is such that the reflector of a common traffic light remains in the traffic light. The colored end pane provided may be left in the traffic light as well.
Traffic signal light emitting devices according to the invention preferably are provided with colored LEDs, e.g. red LEDs for a red traffic light segment, green LEDs for a green traffic light segment and yellow LEDs for a yellow traffic light segment. On the other hand, it is also possible with the invention to make use of white LEDs, not only for traffic signal light emitting devices, but especially for lighting systems.

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The invention preferably does not make use of a pulse circuit in order to operate the LEDs with mains voltage.
It is emphasized that numerous features of the invention may also be realized with a light emitting device that is not designed for connection to a mains voltage of at least 110 V, but e.g. for a proprietary voltage below 110 V, preferably in the range from 24 to 110 V.

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The invention and preferred embodiments of the invention will be explained in more detail hereinafter by way of embodiments shown in theaccompanying/drrawings in wnich
Fig. 1 shows a traffic signal light emitting device, in a side view and partly in a longitudinal sectional view;
Fig. 2 shows part of a traffic signal light emitting device of alternative design, in a longitudinal sectional view;
Fig. 3 shows part of a traffic signal light emitting device of alternative design, in a partial longitudinal sectional view;
Fig. 4 shows a circuit diagram for the LEDs and the current limiting means for the LEDs in a light emitting device;
Fig. 5 shows a circuit diagram for the LEDs and the current limiting means for the LEDs in a light emitting device, with the current limiting means being realized in the form of a current impression means.
Fig. 1 illustrates, in a longitudinal sectional view containing the optical axis 2, part of a traffic light segment (either a green traffic light segment or a yellow traffic light segment or a red traffic light segment), viz. a front portion of a reflector 4 and a forward, colored end pane 6. In the cut-away rear portion of the reflector 4, the reflector 4 carries a screw-type socket in which an incandescent bulb is threadedly mounted in a common traffic light segment. The reflector 4 has its front end portion attached to a housing of the respective traffic light segment, as indicated in Fig. 1 by way of a front end flange 8 of reflector 4 and axes 10 of mounting screws.
the incandescent bulb usually present in a traffic light segment operated with an incandescent bulb has been threadedly removed, and instead of the latter a traffic signal light emitting device 20 as illustrated has been threadedly mounted in the same socket. In the front end portion thereof (at the top in Fig. 1), the light emitting device 20 becomes larger in size so as to correspond almost to the

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inner diameter of the reflector 4 at the front end portion thereof. At that location, the light emitting device 20 has a rubber ring 22 attached thereto, which is supported in a circumferential groove of the light emitting device 20. The outer diameter of the ring 22 and the axial positioning of the same (optical axis 2 = longitudinal central axis of light emitting device 20) are matched such that, when the light emitting device 20 is completely threadedly engaged in the screw-type socket (not shown), the ring 22 has a rear end portion of its outer circumference abutting the inside of the reflector 4, thereby providing for additional stabilization of the light emitting device. Via the screw-type socket, not shown, the light emitting device 20 is connected to a mains voltage of e.g. 110 V or 230 V in the same manner as an incandescent bulb,
In the front end portion {at the top in Fig. 1), the light emitting device 20 carries a circuit board 24 extending at right angles with respect to the axis 2. The circuit board 24 has an outer diameter only slightly smaller than that of the largest inner diameter of the reflector 4. On the front side of the circuit board 24, there is mounted a multiplicity of LEDs 30. The rear side of the circuit board 24 has circuit components 32 mounted thereon. An embodiment of an LED assembly and a circuit will still be described further below. In this place, it is merely pointed out that the circuit permits operation of the LEDs 30 with the mains voltage, without voltage conversion and without pulse modulation.
The traffic signal light emitting device 20 illustrated and described thus is composed of a - roughly speaking - mushroom-shaped supporting body 34 and the afore-mentioned circuit board 24 along with the LEDs 30 and circuit components 32 mounted thereto. The supporting body 34 preferably is made of plastics material and is manufactured preferably by injection molding. The rear end portion of the supporting body 34 having the screw-type thread constitutes a mounting portion for mounting the light emitting device; the front end portion of the supporting body 34, supporting the circuit board 24, constitutes a light emitting portion of the light emitting device 20.
The broken line illustrates a translucent end plate 36 of the light emitting device 20, which may be provided optionally.

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Fig. 2 illustrates an alternative in which a front circuit board 24a and a rear circuit board 24b are provided instead of circuit board 24. The circuit boards 24a and 24b constitute a sandwich-like circuit board assembly 38. The front circuit board 24a carries the LEDs 30 and components 32a which, in terms of circuit technology, are to be positioned most expediently closely adjacent to the LEDs 30 (in particular Zener diodes and capacitors, cf. the description further below). The rear circuit board 24b carries the remaining components 32b. The circuit boards 24a and 24b are electrically connected to each other via plug connectors 40.
Fig. 3 illustrates a length-adjustable portion 42 of a supporting body of a light emitting device 20. A cylindrical rear portion 44 of the supporting body projects into a front portion 46 of the supporting body of somewhat larger diameter, in the fashion of a telescope-type connection. The rear portion 44 has a radially outwardly projecting pin 48 attached thereto. This pin 48 cooperates with a groove or a slot 50 which, in the cylindrical front portion 46, is provided along a spiral path, analogous to a thread. Upon rotation of the portions 44 and 46 relative to each other, the effective length of the supporting body, as measured in the direction of the axis 2, changes. The fit between the front portion 46 and the rear portion 44 is so tight that a once set longitudinal adjustment does not change by itself. Optionally, there may be provided a friction-enhancing intermediate ring between the portions 46 and 44. The length-adjustable portion 42 is located in that part of the supporting body that is referenced 52 in Fig. 1.
Fig. 4 schematically illustrates a circuit arrangement according to an embodiment of the invention.
Block 114 shows a circuit unit of an embodiment of the light emitting device according to the invention, consisting of power or mains input 103, rectifier 108, current-limiting circuit 106, diode D, LED strand 102, capacitor C1, capacitor CN+1,and resistor R4.

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The rectifying circuit 108 serves to convert an alternating voltage possibly applied to the mains input into a direct voltage, which consequently is applied between points 118 and 110. Without excluding other embodiments, the present embodiment makes use of a bridge-type rectifier.
Block 102 has LEDs (LED 1 to LED N) connected in series, with Zener diodes (ZD 1 to ZD N) being connected in anti-parallel fashion and capacitors (C 2 to C N) being provided in parallel. Without excluding other embodiments, the present embodiment has for each LED (LED 1 to LED N) one capacitor (capacitor C2 to C N) connected in parallel thereto and for each group of four LEDs (LED 1 to LED N) one Zener diode connected anti-parallel thereto. In the present embodiment, the forward voltage of the LEDs (LED 1 to LED N) is approx. 3.5 volts each, with 31 diodes being arranged in series. The breakthrough voltage of the Zener diode (ZD 1 to ZD N) is higher than the sum of the forward voltages of the respective light emitting diodes (LED 1 to LED N) bridged in anti-parallel manner. This ensures the current flow across the Zener diode (ZD 1 to ZD N) in case a failure arises in the light emitting diodes (LED 1 to LED N) bridged in anti-parallel manner, the supply lines to the same or the solder connections thereof.
Depending on the wavelength, the LEDs typically have a forward voltage of 2 to 4 V and are selected e.g. with a nominal current of 50 mA. The maximum admissible power loss of the Zener diodes has to be at least as large as the product of Zener voltage and nominal current through the LEDs.
Diode D, in forward direction, is located between the rectifier circuit 108, i,e. potential 108, and the LED strand 102, i.e. potential 104.
Block 106 illustrates the current-limiting circuit of an embodiment of the light emitting device. It is realized by an npn transistor and the resistors Rl, R2 and R3. The resistors R1 and R2 are connected in series between the potentials 118 and 110. The transistor T1 has its base connected to the potential between the resistors R1 and R2. The emitter of transistor T1 is connected to the potential 110. The collector of transistor T1 is connected to the potential 104 via the

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resistor R3 and the LED strand 102 connected in series therewith and including the LEDs LED1 to LEDN. The base voltage is set via the resistors R1 and R2, thereby determining the collector current on the basis of the characteristics of the transistor. In the present embodiment, the resistor R1 is set to a value of approx. 100 kiloohms, resistor R2 is set to a value of approx. 10 kiloohms, and resistor R3 is set to a value of approx. 100 ohms. The transistor used is of the type MPSA 42. The current-limiting circuit may be composed, for example, of a MOSFET transistor as well. In both cases described, the current limitation is obtained by means of the resistor R3. The transistor has the function of an electronic switch.
The circuit described may be composed in equivalent manner by means of a pnp bipolar transistor. !n that case, the emitter thereof has the potential (104) of the anode of diode (D) connected thereto, the collector thereof is connected to the opposite mains voltage potential via the LED strand (102), and the base thereof is connected to the potential of the mains voltage.
The capacitor C1 is connected in parallel to the LED strand 102 between the potentials 104 and 110. The capacitor C1 serves to smooth the half-waves of the rectified alternating voltage, so that the LEDs have a quasi continuous direct voltage supplied thereto.
The capacitor CN + 1 is connected in parallel to the LED strand 102 between the potentials 118 and 110. When the circuit is connected to mains voltage, capacitor CN+1 makes sure that the voltage divider 12 at the base of transistor T1 approximately has the peak voltage supplied thereto between the peaks of the half-waves. It is thus ensured that the transistor T1 connects through between the peaks of the half-waves and that the LEDs may emit light as these also have current supplied thereto via capacitor C1.
For preventing persistence or afterglow upon deactivation of the mains voltage 103, the present embodiment provides a discharge resistor R4 connected in parallel to capacitor C1, and the diode D separates the voltage divider of the

18/25
base of transistor T1 from the potential 104 of capacitor C1, whereupon the transistor blocks the current flow through the diodes.
Provided upstream of the rectifier at the mains input, there may be an optional voltage divider circuit permitting the light emitting unit to be easily reconfigured for different mains voltages.
The circuit depicted in block 116 corresponds exactly to the above-described circuit in block 14 and is of redundant construction to the above-described circuit starting from the mains input.
The circuit illustrated in Fig. 5 differs from the circuit illustrated in Fig. 4 merely in the following respect:
Instead of resistor R2, there is provided a diode Dref. Resistor R3 has been omitted. A resistor R13 and a capacitor CD are newly provided. The capacitor CD is connected in parallel to the diode Dref.
The embodiment according to Fig. 5 has a current impression means. The control is realized by way of resistor R1 and the forward biased diode Dref. Located in series with the LED strand are the collector-to-emitter path of the npn bipolar transistor T1 and the resistor R13. The base voltage of the transistor T1 is tapped by diode Dref. The sum of the voltage drop across R13 and of the voltage drop across the base-to-emitter path of T1 corresponds to the voltage across the diode Dref. As the voltage drop across the diode Dref is independent of the mains voltage to the largest possible extent, the current flowing through resistor R13 thus is independent of the same, so that the current flowing through the LEDs is independent of the mains voltage to the largest possible extent as well. The resistor R13 should be dimensioned such that the quotient of the voltage across the diode Dref minus the voltage across the base-to-emitter path, divided by the resistance of resistor R13, yields substantially the nominal current of the LEDs. An npn bipolar transistor T1 is to be chosen such that the mains voltage may be present across the collector-to-emitter path and such that the current set can flow through the LEDs across the collector-

19/25
to-emitter path. The diode Dref can be realized by a forward biased LED or a forward biased diode or a reverse biased Zener diode. Transistor T1 may also be realized by a field effect transistor. For generating a constant current, a constant current diode may be used as well. The diode Dref and the resistor R1 may also be replaced by a reference voltage source.
In the circuit described, the transistor has a function in the current impression means and in the afterglow suppressing means.
The circuit described may be composed in equivalent manner by means of a pnp bipolar transistor.

20 WE CLAIM :
1. A light emitting device, in particular a traffic signal light emitting device, composed with
light emitting diodes (=LEDs) (30),
comprising the following features :
(a) the light emitting device comprises at least one strand (102) having a multiplicity of LEDs
(30) connected in series;
(b) the LED strand (102) is adapted to be connected substantially to a mains voltage (103) of
at least 110V without voltage conversion and without pulse modulation;
(c) the LED strand is adapted to be connected to the mains voltage via a current limiting
means (106); and
(d) there is provided a means for suppressing afterglow (R4, D, Tl) of the LEDs (30).
2. A light emitting device as claimed in claim 1, wherein LED strand (102) has a plurality of
Zener diodes (ZD) provided therein, each being connected in parallel to at least one LED (30) and
being reverse biased.
3. A light emitting device as claimed in claim 1 or 2, wherein the LED strand and the current
limiting means (106) are adapted to be connected to the mains voltage (103) via a rectifying circuit
(108).
4. A light emitting device as claimed in any of claims 1 to 3, wherein the assembly of the LEDS
(30) and the power supply of the LEDs (30) are redundant starting from the mains input.

21
5. A light emitting device as claimed in any of claims 1 to 4, wherein
(a) a supporting body (34) having a mounting portion for supporting the light emitting device
(30) in a socket supplying power to the same, and having a light emitting, portion equipped with
LEDs (30);
(b) and a circuit board (24) or a sandwich - like circuit board assembly (24a, 24b), with the
LEDs (30) and the components (32) of a circuit that permits connection of the light emitting device
(20) to a mains voltage of at least 110V without voltage conversion being mounted on said circuit
board (24) or said sandwich-like circuit board assembly (24a, 24b).

6. A light emitting device as claimed in claim 5, wherein the LEDs (30), in terms of the spacing
thereof from the mounting portion of the supporting body (34), are positioned such that the light
emission thereof is largely equivalent to the light reflected by a reflector (4) of a common traffic
light.
7. A light emitting device as claimed in claims 5 or 6, wherein the supporting body (34), except
for parts of the mounting portion, consists of plastics material.
8. A light emitting device as claimed in any of claims 5 to 7, wherein the supporting body (34)
has a configuration of substantially circular cross-sectional area.
9. A light emitting device as claimed in any of claims 5 to 8, wherein the circuit board assembly
(24a, 24b), as seen in plan view, has a diameter which substantially corresponds to the front end
diameter of the reflector (4) of a common traffic light.

22
10. A light emitting device as claimed in any of claims 5 to 9, wherein the mounting portion fits
into a common screw - type socket provided for a particular incandescent bulb, or into a common
plug- in socket or a common bayonet-type socket.
11. A light emitting device as claimed in any of claims 5 to 10, wherein the supporting body is
provided with a translucent end plate (36) in front of the LEDs (30).
12. A light emitting device as claimed in any of claims 5 to 11, wherein the supporting body (34)
comprises an abutment ring (22) for abutment on an abutment portion of an apparatus in which the
light emitting device (20) is to be inserted.
13. A light emitting device as claimed in any of claims 5 to 12, wherein the supporting body (34)
has a length-adjustable portion (42) by adjustment of which the positioning of the LEDs (30) with
respect to the mounting portion of the supporting body (34) can be adjusted.
14. A light emitting device as claimed in any of claims 1 to 13, wherein the current limiting
means (106) comprises a resistor (R3).
15. A light emitting device as claimed in any of claims 1 to 14, wherein the current limiting
means (106) comprises a current impression means.
16. A light emitting device as claimed in claim 15, wherein the current impression means (106)
comprises a resistor (Rl) and a diode (Dref) that are connected in series to the mains voltage (103),

23
the resistor (Rl) being connected to the same potential (118) of the mains voltage (103) as the LED strand (102), and the diode (Dref) being connected to the opposite potential (110) of the mains voltage (103), and comprises furthermore a transistor (Tl), with the base thereof having the potential between the resistor (Rl) and the diode (Dref) applied thereto, the collector thereof being connected via the LED strand (102) to the said same potential (118) of the mains voltage (103), and the emitter thereof being connected, via an additional resistor (R13), to the opposite potential (110) of the mains voltage (103).
17. A light emitting device as claimed in any of claims 1 to 16, wherein there is at least one
capacitor (Cl) connected in parallel to the LED strand (102) comprising the current limiting means
(106).
18. A light emitting device as claimed in claim 17, wherein a forward biased diode (D) is located
between the rectifying circuit (108) and the capacitor (Cl), and in that an electronic switch (Tl)
having at least one control input is provided in series with the LED strand (102) connected to the
anode of the diode (D), said at least one control input of the electronic switch (Tl) being connected
to the mains voltage (103).
19. A light emitting device as claimed in claim 18, wherein the electronic switch is constituted
by a transistor (Tl), the collector thereof being connected via the LED strand (102) to the potential
(104) of the anode of the diode (D), the emitter thereof being connected to the mains voltage
potential (110) opposite thereto, and the base thereof being connected to the potential (118) of the
mains voltage.

24
20. A light emitting device as claimed in any of claims 1 to 19, wherein there is provided at least
one component (Tl) having a function both in the current limiting means (106) and in the means for
suppressing afterglow (R4, D, Tl) of the LEDs (30).
21. A light emitting device as claimed in any of claims 17 to 20, wherein the capacitor (Cl) has
at least one resistor (R4) connected in parallel thereto.
22. A light emitting device as claimed in any of claims 1 to 21, wherein the LEDs (30) of the
LED strand (102) have at least one capacitor (C2 to CN) connected in parallel thereto, with each
capacitor (C2 to CN) being connected in parallel to at least one LED (30).
23. A light emitting device as claimed in any of claims 4 to 22, wherein the LEDs (30) of the
redundant LED strands (102) are mounted on the circuit board (24) or the sandwich-like circuit board
assembly (24a, 24b) such that a substantially homogeneous emission of light is obtained in case of
failure of a redundant part (104, 116).
24. A light emitting device as claimed in any of claims 4 to 22, wherein the LEDs (30) of the
redundant LED strands (102) are arranged on the circuit board (24) or the sandwich-like circuit board
assembly (24a, 24b) such that, in case of failure of a redundant part (114, 116), such non-
homogeneous emission of light arises that the failure becomes recognizable to an observer.
There is disclosed a light emitting device, in particular a traffic signal light emitting device, composed with light emitting diodes (=LEDs) (30), said device having at least one strand (102) with a multiplicity of LEDs (30) connected in series; said strand being adapted to be connected via a current limiting means, substantially to a mains voltage of at least 110V without voltage conversion and without pulse modulation; and having a means for suppressing afterglow of the LEDs (30).

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Patent Number

207730

Indian Patent Application Number

00074/KOLNP/2005

PG Journal Number

25/2007

Publication Date

22-Jun-2007

Grant Date

21-Jun-2007

Date of Filing

20-Jan-2005

Name of Patentee

MONZO, JOSE.

Applicant Address

STETTENER STRASSE 32, 73732 ESSLINGEN

Inventors:

#	Inventor's Name	Inventor's Address
1	MONZO, JOSE.	STETTENER STRASSE 32, 73732 ESSLINGEN

PCT International Classification Number

G08G1/095

PCT International Application Number

PCT/EP2003/006774

PCT International Filing date

2003-06-26

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	102 35 811.7	2002-08-05	Germany
2	102 28 820.8	2002-06-27	Germany