J.
This is to ensure DC doesn't drive the FETs and blow them up in the
event that for some reason the exciter stops and the driver provides a
constant DC signal to the FETs gate. This clamping type arrangement is
to ensure only + going pulses drive the FETS and this is a critical FET
safety feature. I have seen designs without it but I'm sure the users
must have a box of spare FETs handy and a warm soldering iron...
Jump into your way back machine and do a circuit analyst of it and
you'll see what I mean. The cap AC couples the drive, the diode ensures
that it is clamped as a + DC pulse train... Therefore, a constant DC
bias on the gate can't happen...
G0MRF was the first I noticed using this technique in amateur design of
2200m class D amps.
73 Scott
PS - check your diode polarity!!!
J. Allen wrote:
Hello Tech types.
While I am working on the amp, I noticed that some of the FET drive
circuits are fed directly from a driver device (G3YXM circuit p66 LF
Today) and some use a blocking capacitor followed by a diode (G0MRF
circuit, p72).
Why are the capacitors and diodes required in one FET circuit and not
in the other?
Thanks,
J.
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