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Parallel Power Transistor Base Drive System

IP.com Disclosure Number: IPCOM000051355D
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Radcliffe, JK: AUTHOR

Abstract

System 10 overcomes the problem of mismatch between two power switching transistors Q1, Q2 driven from a common voltage source, i.e. driver 11 and transformer T1.

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Parallel Power Transistor Base Drive System

System 10 overcomes the problem of mismatch between two power switching transistors Q1, Q2 driven from a common voltage source, i.e. driver 11 and transformer T1.

More specifically, a low-cost matching second transformer T2 couples the respective bases of transistors Q1 and Q2. Flux balance in transformer T2 matches the base currents during turn-on time. Transformer T1 interacts with the average voltage of transistors Q1 and Q2. Transformer T2 does not dissipate any substantial power and hence place any additional requirements on the driver source 11.

Low-cost, low-voltage diodes D1 and D2 are used during the turn-off transient period. During this time period, reverse base currents are drawn from transistors Q1 and Q2 as stored base charge is removed. As long as base currents are present, transformer T2 produces a current balance. However, due to device mismatch, one of the transistors Q1 and Q2 turns off first. When this occurs, the balanced current is zero, and transformer T2 becomes an open circuit.

The secondary voltage of transformer T1 falls until the particular diode D1 or D2 (i.e., the one connected to the remaining turned-on transistor Q1 or Q2) turns on. As a result, the circuit of the still turned-on one of the transistors Q1 and Q2 is completed until its base charge is completely removed and the particular transistor turns off. After both transistors Q1 and Q2 are turned-off, the voltage of transformer T2 re...