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Switching Regulator Off Drive

IP.com Disclosure Number: IPCOM000077782D
Original Publication Date: 1972-Sep-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Duspiva, WS: AUTHOR

Abstract

Transistor switching losses in a switching regulator operated at high frequencies, such as 20 khz can be quite large. By placing a resistor in series with the inductor in a switching regulator L/C network, a voltage point for providing an almost constant off-drive may be derived.

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Switching Regulator Off Drive

Transistor switching losses in a switching regulator operated at high frequencies, such as 20 khz can be quite large. By placing a resistor in series with the inductor in a switching regulator L/C network, a voltage point for providing an almost constant off-drive may be derived.

In one typical form of switching regulator, transistor T1 is provided with ON- DRIVE pulses to its base so as to deliver current pulses through its collector- emitter circuit to an output circuit having an inductor L, a capacitor C, a free- wheeling diode D1 and a load R2. In many circuits of this kind, a resistor R1 is connected from base to emitter of T1 to provide off-drive (reverse base drive) for T1. In such a case, without R3, the Vbe of T1 determines the amount of off-drive for T1. As T1 begins to turn off, the Vbe drops in voltage and the off-drive is consequently reduced, slowing down the fall time, and causing large losses.

With the addition of R3, the off-drive is less of a function of Vbe of T1. L and D1 operate to fix inductor current IL through R3 at an almost constant value. Accordingly, R1 is returned to an almost constant negative voltage. The result is to reduce markedly the fall-time of the T1 collector-emitter current, thereby reducing losses in T1.

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