Title of Invention

A CIRCUIT ARRANGEMENT FOR IGNITING AND OPERATING A HIGH-PRESSURE DISCHARGE LAMP

Abstract The invention relates to a circuit arrangement for igniting and operating a high-pressure discharge lamp, provided with input terminals for connection of a supply source, output terminals for connection of the lamp, switching means for operating the lamp at a nominal lamp voltage V1a during stable lamp operation and for generating an open voltage Vo at the output terminals before the lamp has ignited, ignition means for generating an ignition voltage pulse when the voltage at the output terminals reaches a threshold value Vi, a control circuit for controlling the switching means. According to the invention, the circuit arrangement is characterized in that the control circuit comprises means for limiting the voltage at the output terminals to a value Vb such that the following is true
Full Text The invention relates to a circuit arrangement for igniting and operating a
high-pressure discharge lamp, provided with
input terminals for connection of a supply source,
output terminals for connection of the lamp,
switching means for operating the lamp at a nominal lamp voltage Via during
stable lamp operation and for generating an open voltage Vo at the output
terminals before the lamp has ignited,
ignition means for generating an ignition voltage pulse when the voltage at the
'output terminals reaches a threshold value Vi.
a control circuit for controlling the switching means.
Such a circuit arrangement is known from BP 0401931 «= US 5,068,572).
The known circuit arrangement is suitable for igniting and operating inter alia high-pressure
sodium lamps and metal halide lamps. These lamps are m general provided with a discharge
vessel in which an electric discharge is maintained during operation and which is enclosed
with intervening space by an outer bulb. These lamps require a high ingition voltage pulse (a
few kV and more). The ignition means become operative through the choice of the open
voltage Vo such that Vo > Vi, and an ignition voltage pulse is generated. The lamp will
ignite then, the voltage across the lamp dropping abruptly to around ten volts. As soon as a
stable discharge has arisen in the lamp, the voltage across the lamp gradually rises up to the
lamp voltage Via accompanying stable lamp operation. The circuit arrangement is so
designed that the lamp voltage Via is lower than the voltage Vi, which in its turn is lower
than the open voltage Vo.
The control circuit of the circuit arrangement ensures that the switching
means ?.ct as a controlled current generator in the stable operational state of the lamp. It is
achieved thereby that no more ignition voltage pulses are generated by the ignition means as
soon as the voltage at the connection terminals drops to the lamp voltage Via or lower.
The generation of ignition voltage pulses for alonger period is
undesirable because this forms a load on the circuit arrangement. It is often suggested in the
literature, therefore, to limit the operation of the ignition means by switching them off after a
certain period has elapsed.
This, however, has a number of disadvantages: .
the comparatively high open voltage Vo remains at the output terminals if the
lamp has not yet ignited,
once the lamp has ignited, the ignition means will generate ignition voltage
pulses the moment the lamp is extinguished, for example upon reaching the end
of its operational life. Especially high-pressure sodium lamps and metal halide
lamps show the characteristic that the lamp will ignite again upon the
application of ignition voltage pulses at the end of its life after extinguishing
and cooling-down. This gives rise to the characteristic flickering behavior of the
lamp. This is unpleasant to observe, but most of all it is detrimental to the
circuit arrangement, while it usually also leads to a considerable amount of
interference radiation (radio interference, etc.).
The invention has for its object to provide a measure for counteracting the
above disadvantages.
According to the,invention, a circuit arrangement of the kind mentioned in
the opening paragraph is for this purpose characterized in that the control circuit comprises
means for limiting the voltage at the output terminals to a value Vb such that the following is
true
Via The choice of the voltage at a level just above the nominal lamp voltage
advantageously realizes that the generation of ignition voltage pulses is suppressed by one
and the same mechanism both in the case of a badly starting lamp and in the case of a lamp
which reaches the end of its life. A further advantage is that a discharge in the outer bulb of
the lamp, either in the form of a glow discharge or in the form of an arc discharge, cannot
be maintained when the discharge vessel of the lamp becomes leaky, so that hazardous
situations are prevented. A particularly suitable embodiment of the means for limiting the
voltage control circuit into a state such that the voltage occurring at the output terminals is limited to
the value Vb. Preferably, the timer is so connected that it is reset upon connection of a
supply source. Preferably, a voltage buffer network is coupled to the timer in order to
prevent the timer from being reset also in conditions where there is a short dip in the supply
voltage delivered by the supply source. This network may be, for example, an RC network.
A downconverter or Buck converter is very suitable for use as the controlled current
generator.
The above and further aspects of^the invention will be explained in more
detail below with reference to/ifcdrawing of an embodiment of a circuit according to the
invention, in which
Fig. 1 shows a circuit arrangement for igniting and operating a high-
pressure discharge lamp,
Fig. 2 shows switching means of the circuit arrangement of Fig. 1 in
detail,
Fig. 3 shows means for limiting the voltage at the output terminals of the
circuit arrangement in more detail, and
Fig. 4 shows an embodiment of the means of Fig. 3 in further detail.
Fig. 1 shows a .circuit arrangement for igniting and operating a high-
pressure discharge lamp, provided with
. input terminals 1 for connecting a supply source,
output terminals 2 for connecting the lamp 3,
switching means II for operating the lamp at a nominal lamp voltage Via during
stable lamp operation and for generating an open voltage Vo at the output
terminals before the lamp has ignited. The circuit arrangement is also provided
with commutator means III for periodically changing the polarity of the current
through the lamp, and with a preconditioner I for generating a DC voltage for
supplying the switching means II. The commutator means also comprise ignition
means (not shown in any detail) for generating an ingition voltage pulse when
the voltage at the output terminals reaches a threshold value Vi. ,.., ....
The circuit arrangement is further provided with a control circuit IV for controlling the S^t-rt-^
switching means, and with means V for limiting the voltage at the output terminals to a value
Vb such that it is true that
Via In an advantageous embodiment, the switching means are constructed as a
downconverter or Buck converter as shown in detail in Fig. 2. In Fig. 2, A and B are
connection points between the switching means and the preconditioner I, and C and D are
connection points with the commutator means III. The downconverter comprises a controlled
semiconductor switch 10, a self-inductance 11, and a freewheel diode 12. The converter is
further provided with a capacitor 13 for reducing ripple on the voltage across the connection
points C, D. A control electrode 101 of switch 1Q is connected to an output 41 of the control
circuit IV. The control circuit has an input 42 for detecting a signal Sv which is proportional
to the voltage at the output terminals and an input 43 for detecting a signal Si which is
proportional to the lamp current. The signal Sv is compared with a reference voltage Vref.
The result of this comparison is conducted to a gate controller 45. The signal Si is conducted
through an integrator to Pulse Width Modulator (PWM) 44, which in its turn sends a
switching signal to the gate controller 45. The control signal generated in the gate controller
45 is conducted to the control electrode 101 through output 41.
The reference voltage Vref forms part of the means for limiting the
voltage at the output terminals to a value Vb such that it is true that
Via The means V are shown in more detail in Fig. 3. The reference voltage
Vref is formed at connection point 52 from an auxiliary voltage Vh by means of a voltage
divider network 50. A switch 51 is included in a branch of the voltage divider network 50
which is connected to connection point 52 at one side. The switch 51 shunts a portion of the
impedance belonging to the voltage divider network. In the embodiment shown, the switch is
accommodated in a branch between connection point 52 and ground. When the switch is
closed, the result will be a lower voltage at connection point 52 compared with the situation
of an opened switch. When the switch is placed between the voltage Vh and connection point
52, a reduction in the voltage at connection point 52 will take place when the switch 51 is
opened. A low voltage at connection point 52 means a low value for the reference voltage
Vref, which results in the gate controller 45 controlling the semiconductor switch such that
the voltage at the output terminals of the circuit arrangement is limited to a comparatively
low value. An embodiment of the means V as shown in Fig. 3 is depicted in further detail in
Fig. 4. The switch is formed by a series arrangement of a diode 55, a timer 500, a voltage
suffer network 53, and a connection point 54 for connecting a supply voltage for supplying
the timer. The switch 51 operates as follows. The moment a supply voltage is connected to
connection point 54, a voltage will be applied to input terminal 501 of timer 500, whereby
the timer is reset. The result of this is that a high signal is present at an output terminal 502
of the timer. This corresponds to the state of a comparatively high voltage at connection
point 52. After a period for which the timer was set has elapsed, the timer switches over and
the vdltage at output terminal 502 becomes low, so that the voltage at connection point 52
also becomes low.
In a practical realization of a circuit arrangement according to the
embodiment described, the circuit arrangement is suitable for igniting and operating a metal
halide lamp, for example of the CDM 35W type, make Philips, with a power rating of 39
W. The lamp has a rated lamp voltage Via of 90 V. When the supply source is connected,
for example a voltage source of 220 V, 50 Hz, the preconditioner supplies a DC voltage of
400 V to the switching means II. The open voltage at the output terminals lies between 310
and 380 V when the lamp has not ignited. The threshold value Vi of the voltage at the output
terminals at which the ignition means start generating ignition pulses is 240 V.
The timer is formed by a type HEF 4541 integrated circuit. The voltage
buffer network comprises a parallel arrangement of a 100 nF capacitor and a zener diode
with a zener voltage of 15 V. The rectified supply source voltage of 220 V serves as the
supply voltage for the timer circuit. To limit the current, a resistor of 300 kO is connected
between connection point 54 and the voltage buffer network. Diode 55 is of the BAV 103
type, make Philips. The value of Vref is 3.3 V when the timer is reset. When the timer
switches over after at most 20 min, Vref drops to 1.5 V, which results in a limitation of the
voltage at the output terminals to a value Vb of at most 200 V. It is clear that the condition
Via is thus complied with.
The timer is so set that it switches over after a minimum of 10 min and a maximum of 20
min. This time is preferably chosen to be so long to provide the possibility of hot re-ignition
of the lamp. The controlled semiconductor switch of the switching means is formed by a
MOSFET, type STP4NA60FI, make SGS-Thomson. The gate controller is an integrated
circuit, type IR2117, make Int. Rectifier. The PMW 44 is an integrated circuit, type
L6560A, make SGS-Thomson.
We Claim :-
1. A circuit arrangement for igniting and operating a
high-pressure discharge lamp, provided with
input terminals for connection of a supply source,
output terminals for connection of the lamp,
switching means for operating the lamp at a nominal lamp
voltage Via during stable lamp operation and for
generating an open voltage Vo at the output terminals
before the lamp has ignited,
ignition means for generating an ignition voltage pulse
when the voltage at the output terminals reaches a
threshold value Vi,
a control circuit for controlling the switching means,
characterized in that the control circuit comprises means (?) for
limiting tiie voltage at the output terminals to a value Vb such
that the following is true



The invention relates to a circuit arrangement for igniting and operating a
high-pressure discharge lamp, provided with
input terminals for connection of a supply source,
output terminals for connection of the lamp,
switching means for operating the lamp at a nominal lamp voltage V1a during
stable lamp operation and for generating an open voltage Vo at the output
terminals before the lamp has ignited,
ignition means for generating an ignition voltage pulse when the voltage at the
output terminals reaches a threshold value Vi,
a control circuit for controlling the switching means.
According to the invention, the circuit arrangement is characterized in that the control circuit
comprises means for limiting the voltage at the output terminals to a value Vb such that the
following is true

Documents:

245-cal-1997-abstract.pdf

245-cal-1997-claims.pdf

245-cal-1997-correspondence.1.1.pdf

245-cal-1997-correspondence.pdf

245-cal-1997-description (complete).pdf

245-cal-1997-drawings.pdf

245-cal-1997-form 1.pdf

245-cal-1997-form 2.pdf

245-cal-1997-form 3.1.1.pdf

245-cal-1997-form 3.pdf

245-cal-1997-granted-abstract.pdf

245-cal-1997-granted-claims.pdf

245-cal-1997-granted-description (complete).pdf

245-cal-1997-granted-drawings.pdf

245-cal-1997-granted-form 1.pdf

245-cal-1997-granted-form 2.pdf

245-cal-1997-granted-specification.pdf

245-cal-1997-others.pdf

245-cal-1997-pa.1.1.pdf

245-cal-1997-pa.pdf

245-cal-1997-reply to examination report.1.1.pdf

245-cal-1997-reply to examination report.pdf

245-cal-1997-specification.pdf


Patent Number 242625
Indian Patent Application Number 245/CAL/1997
PG Journal Number 36/2010
Publication Date 03-Sep-2010
Grant Date 02-Sep-2010
Date of Filing 13-Feb-1997
Name of Patentee KONINKLIJKE PHILIPS ELECTRONICS N. V.
Applicant Address GROENEWOUDSEWEG 1, 5621 BA EINDHOVEN
Inventors:
# Inventor's Name Inventor's Address
1 FRANCISCUS HUBERTUS THEODORUS LAMMERS KANTSINGEL 24, 5349 AJ OSS
2 OSCAR JAN DEURLOO GROENEWOUDSEWEG 1, 5621 AE EINDHOVEN
PCT International Classification Number H05B 37/02
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA