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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.
English (United States)
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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
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
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...