Browse Prior Art Database

Turnoff Circuit

IP.com Disclosure Number: IPCOM000095984D
Original Publication Date: 1964-Nov-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Norton, DE: AUTHOR

Abstract

An auxiliary transistor speeds turnoff of a driver transistor. Such is effected by amplifying the turnoff transient of a coupling transformer and using the resulting signal to short the emitter base junction of the driver.

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Turnoff Circuit

An auxiliary transistor speeds turnoff of a driver transistor. Such is effected by amplifying the turnoff transient of a coupling transformer and using the resulting signal to short the emitter base junction of the driver.

Transistor 1, the driver transistor, conducts when a signal produced by transistor 2 is coupled to its base via transformer 3. Auxiliary transistor 4 helps turn off driver transistor 1. Transistor 4 responds to the reverse current transient of transformer 3 to provide a momentary short circuit to the emitter-base junction of transistor 1 at turnoff time.

Transistor 4 is off while transistors 1 and 2 are conducting. Transistor 2 is turned off to turn off driver transistor 1, but minority carriers in transistor 1 attempt to maintain it conducting. Transformer 3, because of flux buildup during the conducting period, provides a momentary reverse current as its primary current stops. This reverse current reversely biases diode 6 and turns on transistor 4 through resistance 5. Transistor 4 momentarily short circuits the emitter-base junction of transistor 1, resulting in quick turnoff.

Transistor 4 thus amplifies the normally present turnoff transient of coupling transformer 3 and applies it to the base-emitter junction of transistor 1 to speed turnoff of transistor 1.

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