# US 4,380,795 A · Base drive circuit for a four-terminal power Darlington

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- Number: US 4,380,795 A
- Document ID: US4380795A
- Status: Granted
- Kind: A
- Application number: 06/246,975
- Filed: 1981-03-24
- Granted: 1983-04-19
- Earliest claimed: 1981-03-24
- Assignees: The United States of America as represented by the United States Department of Energy
- Inventors: Fred C. Lee; Roy A. Carter
- Web page: https://patentgrep.com/patent/US4380795A

## CPC

- H03K 17/615: in a Darlington configuration
- H02M 7/5387: in a bridge configuration
- H03K 17/04126: {in bipolar transistor switches}
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)

## Abstract

A high power switching circuit which utilizes a four-terminal Darlington transistor block to improve switching speed, particularly in rapid turn-off. Two independent reverse drive currents are utilized during turn off in order to expel the minority carriers of the Darlington pair at their own charge sweep-out rate. The reverse drive current may be provided by a current transformer, the secondary of which is tapped to the base terminal of the power stage of the Darlington block. In one application, the switching circuit is used in each power switching element in a chopper-inverter drive of an electric vehicle propulsion system.

## Claims

### Claim 1

An electrical power switching device, comprising:
a. a four-terminal power Darlington including a first driver transistor stage having a first base and a second power transistor stage having a second base coupled to the emitter of said first transistor stage; and
b. means for respectively applying first and second independent reverse currents to the emitter-base junctions of said first and second transistor stages so as to independently sweep the minority carriers out of said emitter-base junctions, thereby turning off said driver stage and said power stage at their own respective sweep-out rates wherein said reverse current applying means includes a current transformer.

### Claim 2 (depends on 1)

An electrical power switching device as in claim 1 wherein said power source comprises the primary winding of said current transformer.

### Claim 3 (depends on 2)

An electrical power switching device as in claim 2 wherein said reverse current applying means comprises means, including a tap off of the secondary winding of said transformer to said second base, for applying a first voltage from said secondary winding across the base-emitter junction of said first driver transistor stage and a second voltage from said secondary winding across the base-emitter junction of said second power transistor stage.

### Claim 4 (depends on 3)

An electrical power switching device as in claim 3 further comprising switch means for applying a prescribed length voltage pulse to said primary.

### Claim 5

In an AC motor drive system including a DC power supply, a power conditioner comprising an inverter for supplying multiphase current to drive the motor and a chopper coupled to the inverter for regulating current to provide torque control to the motor, the chopper and inverter including a plurality of electrical power switching devices, each device including:
a. a four-terminal power Darlington including a first driver transistor stage having a first base and a second power transistor stage having a second base coupled to the emitter of said first transistor stage; and
b. means for respectively applying first and second independent reverse currents to the emitter-base junctions of said first and second transistor stages so as to independently sweep the minority carriers out of said emitter-base junctions, thereby turning off said driver stage and said power stage at their own respective sweep-out rates, said reverse current applying means including a current transformer.

### Claim 6 (depends on 5)

In the AC motor drive system of claim 5, wherein said reverse current applying means comprises means, including a tap off of the secondary winding of said transformer to said second base, for applying a first voltage from said secondary winding across the base-emitter junction of said first driver transistor stage and a second voltage from said secondary winding across the base-emitter junction of said second power transistor stage.