Title of Invention

CONSTANT POWER BATTERY CHARGER

Abstract

Abstract of the Disclosure A power supply for a rechargeable battery in a portable computer system is disclosed which adjusts the level of charging current depending upon the current drawn by the portable computer system. The power supply includes an AC adapter which supplies input current for operating the computer system and for charging the battery. Sensors are connected to the AC adapter, the battery, and an output of the power supply to detect the level of input current from the AC adapter, the level of charging current supplied to the battery, and the output voltage level of the power supply. A controller is connected to each of the sensors and monitors the input current level, the charging current level, and the output voltage level. The controller generates a control signal which indicates whether any one of the levels has exceeded a respective predetermined maximum value. A charging current control circuit is connected to the controller and to the battery and controls current flow between the AC adapter and the battery based upon the control signal generated by the controller. When the computer draws less current, the battery charging current is increased accordingly, thus using all of the power output from the AC adapter-

Full Text

The invention relates to battery chargers and, in particular, to a system for charging a rechargeable battery in a portable computer. Portable or laptop computers are commonly provided with rechargeable batteries which power the computer when conventional power outlets are not available. An AC adapter is also typically provided to power the computer when the user does have access to an outlet and the batteries are not sufficiently charged. The AC adapter further provides power to a battery charging power supply which recharges the batteries. In most portable computer systems, the power supply supplies two levels of battery charging current: one level when the computer system is off and a second when the computer system is on. To ensure that there is always sufficient current available for charging the battery, the level of charging current output by the battery charger when the system is on must be selected in accordance with the maximum current which could be drawn by the system. Thus, the AC adapter must be designed for the situation in which the computer is using maximum power and the battery requires charging. Because the adapter is designed for this "worst case" situation, the size of the AC adapter is often larger than necessary for typical operation where the computer is not drawing the maximum current and the balance of power supplied by the AC adapter is wasted. Alternatively, some systems utilize a constant current AC adapter to charge the battery. The output of the Ac adapter is directly connected to the battery and to the DC/DC power supply which powfers the computer system. In this manner, the battery charging power supply is eliminated-and all of the current from the adapter that is not used by the computer system is available to charge the battery. However, in this configuration, the output voltage of the adapter is clamped to the battery voltage and the output capabilities of the adapter are significantly reduced. For example, if the AC adapter was rated at 20 Volts with a constant current of 1 amp, the output power of the adapter would be 20 Watts. If a 10 Volt battery was connected to the output of the adapter, the output capacity of the adapter would be reduced by half to 10 Watts. Summary of the Invention The present invention provides a power supply for a rechargeable battery that adjusts the battery charging current depending upon the current drawn by the portable computer system. The power supply includes a switching regulator which monitors the input current from an AC adapter. When the computer draws less current, the battery charging current is increased accordingly, thus using all of the power output from the AC adapter. The invention provides a power supply for recharging a battery in a portable computer system. The power supply comprises an AC adapter which supplies input current for operating the computer system and for charging the battery. A first sensor is connected to the AC adapter which detects the level of input current from the AC adapter. A second sensor is connected to the battery which detects the level of charging current supplied to the battery. A third sensor is connected to an output of the power supply which detects the output voltage level of the power supply. A controller is connected to each of the sensors and monitors the input current level, the charging current level, and the output voltage level. The controller generates a control signal which indicates whether any one of the levels has exceeded a respective predetermined maximum value. A charging current control circuit is connected to the controller and to the battery and controls current flow between the AC adapter and the battery based upon the control signal generated by the controller. The first sensor may comprise-- a resistor connected between the AC adapter and a DC/DC converter which supplies operating power for the computer system. The second sensor may comprise a resistor connected between the battery and a ground reference. The third sensor may comprise a capacitor connected to the output of the power supply. The charging current control circuit may include a transistor connected to the AC adapter and to the battery, wherein the transistor is biased on and off in accordance with the control signal generated by the controller to control current flow between the AC adapter and the battery. The power supply may further comprise a filter connected between the charging current control circuit and the battery which filters the charging current supplied to the battery. Another aspect of the invention is a regulator for controlling current flow between an AC adapter and a battery in a portable computer system. The regulator comprises a controller connected to the AC adapter, the battery, and an output of the regulator to monitor a first input signal indicative of an input current level supplied by the AC adapter, a second input signal indicative of a charging current level supplied to the battery, and a third input signal indicative of an output voltage of the regulator. The controller generates an output signal which indicates whether any of the input signals has exceeded a respective predetermined maximum value. A charging current control circuit is connected to the controller and to the battery and supplies current from the AC adapter to charge the battery when the output signal from the controller indicates that none of the input signals are above the respective predetermined maximum values. The charging current control circuit may include a transistor connected between the AC adapter and to the battery, wherein the transistor is biased on and off in accordance with the output signal generated by the controller to control current flow between the AC adapter and the battery. The regulator may further comprise a driving circuit connected between the' controller and the charging current control circuit for driving the transistor. The regiilator may also comprise a filter connected between the charging current control circuit and the battery which filters the charging current supplied to the battery. Another aspect of the invention is a power supply for recharging a battery in a portable computer system. The power supply comprises an AC adapter which supplies input current for operating the computer system and for charging the battery. An input current sensing circuit is connected to the AC adapter which detects the level of input current from the AC adapter and generates a voltage indicative of the input current level. A charging current sensing circuit is connected to the battery which detects the level of charging current supplied to the battery and generates a voltage indicative of the charging current level. An output voltage sensing circuit is connected to an output of the power supply which detects a voltage indicative of an output voltage level of the power supply. A controller is connected to each of the sensing circuits and compares the input current level, the charging current level, and the output voltage level with a respective predetermined maximum value. The controller generates a control signal which indicates whether any one of the levels has exceeded the respective predetermined maximum value. A charging current control circuit is connected to the controller and to the battery and controls current flow between the AC adapter and the battery based upon the control signal generated by the controller. The input current sensing circuit may include a resistor connected between the AC adapter and a DC/DC converter which supplies operating power for the computer system. The charging current sensing circuit may include a resistor connected between the battery and a ground reference which senses a voltage proportional to the charging current. The output voltage sensing circuit may include a capacitor connected to the output of the power supply. Yet another aspect of the invention is a method of regulating thd amount of charging current supplied to a rechargeable battery by a regulator in a portable computer system including an AC adapter which supplies input current for operating the computer system and for charging the battery. The method comprises the steps of sensing the level of input current supplied by the AC adapter; sensing the level of charging current supplied to the battery; sensing the level of an output voltage of the regulator; monitoring the input current level, the charging current level, and the output voltage level; generating a control signal which indicates whether any one of the levels has exceeded a predetermined maximum value; and controlling current flow between the AC adapter and the battery based upon the control signal. Accordingly the present invention provides a battery charging apparatus having an input current supplied by an external source and having a charging output that provides a charging current to a battery that supplies operating current to circuitry in a portable computer, battery charging apparatus comprising : a controller connected to receive a first input signal indicative of a level of the input current supplied by the external current source, connected to receive a second input signal indicative of a level of the charging current supplied to the battery, and connected to receive a third input signal indicative of an output voltage on the output that provides the charging current to the battery, the controller responsive to the first, second and third input signals to generate a control signal that has a first state at an inactive level when any one of the first, second and tliird input signals exceeds a respective first, second and third limit value and that has a second state at a variable active level when none of the first, second and third input levels exceed the respective first, second and third limit values; and a charging current control circuit connected to the controller and to the battery, the charging current control circuit responsive to the control signal from the controller to supply the charging current from the external current source to charge the battery when the control signal from the controller has the second state at the variable active level, the controller varying the active level of the second state to cause the first input level to be maintained approximately at the first limit value regardless of changes of the operating current provided to the circuitry in the portable computer as long as the second input signal and the third input signal are below the respective second limit value and third limit value. With reference to the accompanying drawings in which Fig. 1 is a block diagram of a battery charging system in accordance with the present invention; Fig. 2 is a schematic diagram of the system of Fig. 1. Figure 1 illustrates a block diagram of a power supply 10 constructed in accordance with the present invention. The power supply 10 supplies charging current to a rechargeable battery 12 which may be used, for example, in a portable or laptop computer system. The computer system includes a constant voltage AC adapter 14 which may comprise a AC/DC adapter connectable to a standard wall socket or a car adapter connectable to a power source, such as a cigarette lighter, in an automobile. The AC adapter 14 is connected to a main DC/DC power supply 16 along a signal Line 18. The DC/DC power supply 16 operates in a conventional manner to provide power for operating various components in the portable computer system. The power supply 10 includes a pulse-width modulated (PWM) switching regulator which monitors the system input current (In^) supplied by the AC adapter 14, the battery charging current (lour), and the output voltage (VOUT) and controls the charging current supplied to the battery 12 from the AC adapter 14 in accordance with these parameters. The PWM regulator comprises a controller 20 and a charging current control circuit which includes a MOSFET 22, a diode 26, an inductor 28, and a capacitor 32. The output O of the regulator controller 20 is connected to the gate of the MOSFET 22. The drain of the MOSFET 22 is connected to the AC adapter output signal line 18 and the source of the MOSFET 22 is connected to a common node 24. The diode 26 is connected between the common node 24 and a ground reference. The inductor 28 is connected between the common node 24 and a common node 30 and the capacitor 32 is connected between the common node 30 and the ground reference. The positive terminal of the battery 12 is connected to the common node 30, while the negative terminal of the battery is connected to a common signal line 34. The power supply further includes a charging current sensor comprising a resistor 36 is connected between the common signal line 34 and the ground reference. The common signal line 34 is also connected to the positive terminal of an output current amplifier 40. The voltage across the resistor 36 is amplified by the output current amplifier 40 to generate an output signal which is indicative of the battery charging current. An input current sensor comprising a resistor 42 is connected in series between the AC adapter 14 and the DC/DC power supply 16. The ends of the current sensing resistor 42 are connected, to the inputs of an input current amplifier 44 which amplifies the voltage across the resistor and generates an output signal which is indicative of the current being drawn by the computer system. The output signals generated by the input and output current amplifiers are effectively OR'ed such that the higher level output signal is input to the regulator controller 20 at INj. The regulator controller 20 further monitors the output voltage by detecting the voltage across an output voltage sensor comprising a capacitor 32. The output voltage is input to the controller 20 via a signal line 46 connected to the regulator controller at INj. The controller 20 generates an output signal at 0 which indi'cates whether any of these parameters has exceeded a respective predetermined maximum^ value. When any parameter is above its respective maximum value, the output level of the regulator controller 20 is high, turning off the MOSFET 22 so that no current from the adapter 14 flows through the MOSFET to the battery 12. If all of the monitored current and voltage parameters are below their predetermined maximum values, the output level O of the regulator controller 20 is low. When the regulator controller output level at O is low, the MOSFET 22 is biased on and any current output by the AC adapter 14 which is not being used by the system is supplied to battery 12. In this manner, the current output by the AC adapter 14 which is not being used by other components in the computer system is available for use in charging the battery 12 and the efficiency of the AC adapter is maximized. Figure 2 illustrates a more detailed diagram of one embodiment of the power supply of the present invention. The regulator controller 20 preferably comprises an integrated circuit (IC) such as the TL594 Pulse-Width Modulation Control Circuit manufactured by Texas Instruments of Dallas, Texas. The IC includes an internal oscillator preferably operating at a frequency of 200KHz and has 2 inputs INi and INj and 2 outputs Oi and O^. As shown, at one end of the input current sensing resistor 42, the adapter output signal line 18 is connected to the positive input terminal of an amplifier 50. The opposite end of the resistor 42 is connected to a common signal line 52. A 4.7KQ resistor 54 is connected between the negative voltage supply terminal of the amplifier 50 and the ground reference and a Zener diode 56 is connected between the resistor 54 and the common signal line 52. A capacitor 58 is connected between the common signal line 52 and the ground reference. A lOOn resistor 60 is connected between the common signal line and the negative input terminal of the amplifier 50. The output of the amplifier 50 is connected to the gate of a MOSFET 62. The source of the MOSFET 62 is connected between the resistor 60 and the negative input terminal of the amplifier 50 while the drain of the MOSFET 62 is connected to a 3.9 KC2 resistor 64. A lO^xF capacitor 66 and a 5.49KQ resistor 68 are each connected between the resistor 64 and the ground reference. The capacitor 66 and resistor 68 are connected in a conventional manner to provide a time constant of T=1/RC. (what purpose?) The positive input terminal of the input current amplifier 44 is connected to a common node 72 between the resistor 64 and the resistor and capacitor 66, 68. The output of the amplifier 44 is connected to the anode of a diode 74. The cathode of the diode 74 is connected to an input INj of the regulator controller 20 via a signal line 76. The negative input terminal of the amplifier 44 is also connected to the signal line 76. As set forth above, the signal line 34 is connected to the positive terminal of the amplifier 40. The negative input terminal of the amplifier 40 is connected to a common signal line 80. A IKQ resistor 82 is connected between the common signal line 80 and the ground reference. A 39Kn resistor 84 and a .33^F capacitor 86 are each connected between the common signal line 80 and the regulator controller input signal line 76. A 15KQ resistor 88 is connected between the regulator controller input signal line 76 and the ground reference. The output of the amplifier 40 is connected to the regulator controller input signal line 76 through a diode 89. The outputs Oi and Oj of the regulator controller 2 0 are connected to the gate of a MOSFET 90. The source of the • MOSFET 90 is connected to the ground reference, while the drain is connected to a 33Q resistor 92. The resistor 92 is connected to a 470n resistor 94 via a common signal line 96. A diode 100 is connected between the resistor 94 and AC adapter signal line 18. The base of a BJT 102 is connected to the common signal line 96 and the emitter is connected to a common node 104. A diode 106 is connected between the common node 104 and the signal line 96. A 4.7KQ resistor 110 is connected at one end to the common node 104 and at the other end to the gate of the MOSFET 22 by a signal line 112. The drain of the MOSFET 22 is connected to the AC adapter signal line 18 and the source is connected to a common signal line 114. A . l^F capacitor 116 is connected between the common signal line 114 and the collector of the BJT 102. A 4.7Kn resistor 118 is connected between a common node 119 and the common signal line 114 and a .33/iF capacitor 120 is connected between the common nodes 104 and 119. The common node 119 is further connected to the signal line 112 via a signal line 122. The Zener diode 26 is connected between the common signal line 114 and the ground reference. The inductor 28, preferably having a value of 22/xH, is connected between the common signal line 114 and the common node 30. The capacitor 32 preferably has a value of .33|xF and is connected between the common node 30 and the ground reference. The sensing resistor 36 preferably has a value of .05Q and is connected between the signal line 34 and the ground reference. As described above, the input current sensing resistor 42 is connected between the AC adapter 14 and the main DC/DC power-supply 16. Thus, the current through the resistor 42 represents the total current being drawn by the system. The resistor 42 is also connected to the positive input terminal of the amplifier 50. The negative input terminal of the amplifier 50 is connected to the resistor 60. As the positive and negative input terminals of the amplifier 50 are virtually the same when the amplifier is operational, the voltage across the resistor 60 is virtually the same as the voltage across the resistor 42. The current through the resistor 60 is output through the operational amplifier 50 and biases the MOSFET 62 on. The current output from the amplifier 60 then flows through the drain of the MOSFET 62 and through the resistors 64 and 68. The MOSFET 50 ensures that substantially all of the current input to the amplifier 50 through the resistor 60 is output from the amplifier through the resistor 68. Because the current through the resistor 68 is the same as the current through the resistor 60 and the voltage across the resistor 60 approximately equals the voltage across the resistor 42,_it follows that the voltage across the resistor 68 is proportional to the voltage across the resistor 42 and therefore is proportional to the current through the resistor 42. Thus, the voltage at the positive input terminal of the amplifier 44 is proportional to the current being drawn by the system. The output current sensing resistor 3 6 is connected to the positive input terminal of the output current amplifier 40 via the signal line 34 and senses a voltage proportional to the battery charging current. The amplifier 40 acts to amplify the voltage across the resistor 36 by a gain factor as provided by the resistors 82 and 84. The amplifiers 40 and 44 are preferable provided on a single IC chip, such as the LM358 Low Power Dual Operational Amplifier manufactured by National Semiconductor of Santa Clara, California. The amplifiers 40 and 44, in combination with diodes 74 and 89, function as a positive peak detector which inputs the highest of the two signals output by the amplifiers to the regulator controller input at INj. As set forth above, a voltage proportional to the battery charging current is input to the amplifier 40, while a voltage proportional to the current being drawn by the system is input to the amplifier 44. When the voltage output of one amplifier is higher than the other, the diode associated with the lower level signal is biased off by the higher level signal and the higher level signal is input to the regulator controller 20 at IN2 through its associated diode. For example, if the voltage output of the amplifier 44 was 3V and the output of the amplifier 40 was 2V, a 3V signal would be input to the regulator controller 20 at IN2. Specifically, because the negative input terminal of the amplifier 40 is tied to the cathode of the diode 89, the diode 89 will initially conduct and keep the voltage at the cathode at 2V. However, the cathode of the diode 89 is also tied to the cathode of the diode 74 and the 3V output of the amplifier 44 and diode 74 acts to back biases the diode 89 and put 3V into the negative input terminal of the amplifier 40. Now, amplifier 40 sees a mismatch where the voltage at the negative input terminal as more positive than the voltage at the positive input terminal. The output of the amplifier 40 is thus inverted which acts to turn off the diode 89. The diode 74 continues to conduct, inputting the higher 3V signal to the regulator controller 20 via the signal 76. The regulator controller 20 continuously monitors the input signal at INj to detect if either the system input current or the battery charging current exceeds a predetermined maximum value. In particular, the voltage proportional to the system input current is monitored to ensure that the input current is limited to the rated current level of the AC adapter 14. The voltage proportional to the battery charging current is also monitored to provide short circuit protection and limit the battery charging current in the event that the output were to shore to ground. Preferably, the regulator limits the system input current to 20 amps and the battery charging current to 3.5 amps. The regulator controller 20 further monitors the output voltage across the capacitor 32 at INj to prevent the output voltage from rising above a predetermined level in the event that the battery is removed from the power supply. Preferably, the regulator ensures that the output voltage does not exceed 15 volts. The regulator controller 20 compares the signals input at inputs INj. and INj with all internal 5V reference signal. The values of the resistors 42, 60, and 68 are selected based on the rated maximum current of the AC adapter 14 such that when the AC adapter current reaches the maximum, the voltage across the resistor 68 is 5V. As set forth above, the resistors 42, 60, and 68 preferably have values of .OSQ, lOOQ and 5.49Kn respectively. Thus, when the input currents is 2.0 Amps, the voltage across the resistor 68 will equal (2 x .05)/l00 = 5 volts. Similarly, the values of the resistors 82 and 84 are chosen to provide again which will amplify the voltage across the resistor 36 to 5V when the maximum battery current is reached. Preferably, the resi'stors provide again factor of 40. Thus, when the maximum battery current of 2.5 amps is reached, the voltage across the resistor 36 will be .13 volts and the amplifier 40 will amplify this voltage to 5 volts. The signal input to the regulator controller at INj is also compared with the internal 5V reference signal. The values of the resistors comprising the voltage divides are selected so that when the output voltage across the capacitor 32 equals 15V, a 5V signal is input at INj. When either input to the regulator controller 20 reaches or exceeds 5V, the output level at O^ or Oj is high, which subsequently biases the MOSFET 22 off and prevents current output by the AC adapter 74 from reaching the battery 12. When the controller inputs are below their respective levels, the output at O^ or Oj is low, subsequently biasing the MOSFET 22 on to conduct current from the AC adapter signal line 18 to the battery 12. Components 90 through 120 act as a driver for the MOSFET 22 as well known to those skilled in the art. When the controller output level is high, the gate to source voltage of the MOSFET 90 is greater than the threshold voltage and the MOSFET is biased on. When the MOSFET 90 is biased on, current from the AC adapter 14 is conducted through the diode 100 and the resistor 94 and directed through the resistor 92 and the MOSFET 90 to the ground reference. Thus, the current at the base of the BJT 102 is below the threshold level and the BJT is biased off. When the BJT 102 is off, the MOSFET 22 is also biased off since the gate to source voltage of the MOSFET is below the threshold. When the MOSFET 22 is off, the diode 26 conducts and the inductor 28 discharges current stored therein through the diode and the capacitor 32. Current is also stored in the capacitor 116 when the MOSFET 22 is off. Conversely, when the regulator controller output level is low, the gate to source voltage of the MOSFET 90 is below the threshold and the MOSFET is biased off. When the MOSFET 90 is off, some of the current from the AC adapter conducted by the diode 100 and resistor 94 is diverted to the base of the BJT 102 since the MOSFET 90 and the diode 92 are effectively open circuits, thereby raising the base current above the threshold so that the BJT 102 conducts and its collector current biases the MOSFET 22 on. When the MOSFET 22 is on, the diode 26 does not conduct and the current from the AC adapter not being used by the system flows through the drain and source of the MOSFET and into the inductor 28 and capacitor 32. Thus, as those skilled in the art will appreciate, the inductor 28 and capacitor 32 act in a conventional manner to filter the charging current supplied to the battery 12. Additionally, when Q6 is turned on, the charge stored by the capacitor 116 is discharged through the BJT 102. The stored charge also serves to turn the diode 100 off so that no current from the AC adapter 14 is conducted by the diode 100. The capacitor 120 and resistor 110 act as a voltage dropping resistor which turns the MOSFET 22 off with a negative voltage when the capacitor 120 is charged to ensure that the maximum gate to source breakdown voltage of the MOSFET 22 is not exceeded. Thus, when the input current, charging current, and output voltage parameters are below their respective maximum values, the power supply of the present invention operates to supply current from the AC adapter which is not being used by the system to the battery to charge the battery. In this manner, when the current drawn by the computer system is less than the maximum, the remainder of the current which can be output by the AC adapter is utilized to charge the battery. This maximizes the efficiency of the AC adapter and reduces the size of the adapter. Although the preferred embodiment of the present invention has been described and illustrated above, those skilled in the art will appreciate that various changes and modifications to the present invention do not depart from the spirit of the invention. For example, other specific implementations of the circuitry in FIG. 1 and FIG. 2 may be used to the current and voltage sensors or the regulator. Accordingly, the scope of the present invention is limited only by the scope of the following appended clai'ms. WE CLAIM: 1. A battery charging apparatus having an input current supphed by an external source and having a charging output that provides a charging current to a battery that supplies operating current to circuitry in a portable computer, battery charging apparatus comprising : a controller connected to receive a first input signal indicative of a level of the input current supplied by the external current source, connected to receive a second input signal indicative of a level of the charging current supplied to the battery, and connected to receive a third input signal indicative of an output voltage on the output that provides the charging current to the battery, the controller responsive to the first, second and third input signals to generate a control signal that has a first state at an inactive level when any one of the first, second and third input signals exceeds a respective first, second and third limit value and that has a second state at a variable active level when none of the first, second and third input levels exceed the respective first, second and third limit values; and a charging current control circuit connected to the controller and to the battery, the charging current control circuit responsive to the control signal from the controller to supply the charging current firom the external current source to charge the battery when the control signal from the controller has the second state at the variable active level, the controller varying the active level of the second state to cause the first input level to be maintained approximately at the first limit value regardless of changes of the operating cunent provided to the circuitry in the portable computer as long as the second input signal and the third input signal are below the respective second limit value and third hmit value. 2. The battery charging apparatus as claimed in claim 1, wherein the external source is a conventional AC adapter having a substantially constant DC output voltage across its first and second terminals which is supplied as the input current. 3. The battery charging apparatus as claimed in claim 1, wherein a first sensor is provided for monitoring the input current supplied by the external source to generate the first input signal. 4. The battery charging apparatus as claimed in claim 3, wherein a DC/DC converter is provided for supplying operating power for the computer system, and wherein the first sensor comprises a resistor connected between the external source and the DC/DC converter. - 5. The battery charging apparatus as claimed in claim 1, wherein a second sensor is provided for monitoring the charging current supplied to the battery to generate the second input signal. 6. The battery charging apparatus as claimed in claim 5, wherein the second sensor comprises a resistor connected between the battery and a ground reference. 7. The battery charging apparatus as claimed in claim 1, wherein a third sensor is provided for monitoring the voltage on the charging output to generate the third input signal. 8. The battery charging apparatus as claimed in claim 7, wherein the third sensor comprises a resistor connected to the output of the battery charging apparatus. 9. The battery charging apparatus as claimed in claim 1, wherein a filter is connected between the charging current control circuit and the battery which filters the charging current supplied to the battery. 10. The battery charging apparatus as claimed in claim 1, wherein the charging current control circuit has a transistor connected to the external source and to the battery, wherein the transistor is biased on and off in accordance with the control signal generated by the controller to control current flow between the external source and the battery. 11. The battery charging apparatus as claimed in claim 1, wherein a driving circuit is connected between the controller and the charging current control circuit for driving the transistor. 12. A battery charging apparatus substantially as herein described with reference to the accompanying drawings.

Documents:

917-mas-1995 abstract.jpg

917-mas-1995 abstract.pdf

917-mas-1995 assignment.pdf

917-mas-1995 claims.pdf

917-mas-1995 correspondence-others.pdf

917-mas-1995 correspondence-po.pdf

917-mas-1995 description (complete).pdf

917-mas-1995 drawings.pdf

917-mas-1995 form-1.pdf

917-mas-1995 form-2.pdf

917-mas-1995 form-26.pdf

917-mas-1995 form-4.pdf

917-mas-1995 form-6.pdf

917-mas-1995 others.pdf

917-mas-1995 petiton.pdf