> Always start out on the dummy load. Test in stages. Test the
driver
> into the FETs with the FET drain supply off. Verify the
waveforms
> with a dual trace scope to see that there's a small 'dead
zone'
> between the two phases. This prevents the possibility
of cross
> conduction. Once the gate waveforms are confirmed to be
correct,
> turn on the FET drain supply. Once the amplifier is verified
to be
> working properly add the
doubler.
Waveforms...
Conditions for all below: Drive is from
the HP 3325B at 2Fo, 5V
square wave, 2.5V DC offset fed into amp driver
board. Amp output
through LPF into a quality dummy load (250W 50 ohm flange
load
resistor known good through UHF).
No drain
voltage...
Gates:
http://www.n1bug.com/gates1.jpghttp://www.n1bug.com/gates2.jpgNow
with 13V on the drains...
Gates:
http://www.n1bug.com/gates1-wdv13.jpghttp://www.n1bug.com/gates2-wdv13.jpgNotice
those have changed a bit with the addition of drain
voltage.
Drains:
http://www.n1bug.com/drains1-wdv13.jpghttp://www.n1bug.com/drains2-wdv13.jpgIt
looks like one phase is "mostly" off before the other is fully
on, but I'm
not sure if this is as much dead zone as I should see?
One is still going
down while the other is starting to come up. In
any case the drain
waveforms don't look good! Suggestions on where
to begin looking for the
cause of this?
Paul
