David
I have been examiming your drive cct from the FET driver to the gate of the
FETs. In this cct you have a cap., a diode with the anode to common this node
connects to a 10ohm resistor in series with the gate that has the gate side
tacked to common via a 4.7k resistor. Am I correct in assuming that the
purpose of the cap is to prevent DC voltages from getting to the gates of the
FETs in the case of an exciter failure? Is the 4.7K just there to keep undue
charge off the gate capacitance? Also, what is the design intent of the 'fast'
diode you have installed. I am also curious as to what the waveform will look
like out of this driver circuit. Is it a 12V p-p from common to 12V or is it
something else.
Thanks for any insight you can offer.
Regards,
Scott, VE7TIL
Quoting [email protected]:
In a message dated 25/05/2004 22:01:42 Central Europe Standard Time,
[email protected] writes:
Maybe somebody has something to say about this......
I think you're spending too much time measuring things at frequencies that
are not LF. It's a great analysis of the detail, but I can't help thinking
you
are overlooking an obvious fault.
BTW. What is the output power? The supply Voltage? and the efficiency?
Just concentrate on the basics. The circuit works, but if you start removing
diodes adding resistors etc, then there's not much anyone can do to help as
you are now developing your own circuit and not trying to duplicate mine.
Build the circuit as close to the original as you can.
Check you have the correct waveforms at the gates. (keep wire lengths short.
This maybe 136kHz, but the waveform rise and fall time neeed to be fast.
Around the HEF4013, FET driver and FETs, the construction should be
consistent
with good VHF practice )
Measure the 136kHz output power, the supply voltage and calculate
efficiency.
Then you'll have a benchmark of performance. If you have less than 200W
output from a 36V supply or an efficiency less than 60% then you have a fault
in
a component or in the construction that you need to find.
After you have a reasonable benchmark, change one thing at a time and
compare. If you have an improvement, leave it in circuit. If you don't, then
put it
back as before and try something else. Jim's work on the transformer is
excellent and I'm now comparing my original transformer with a version of
Jim's
built on a 3C90 42mm core as supplied in the kit.
I've built versions of this circuit from 400W at 73k to 700W (4 FETs) at
136kHz. There's even a version running in the Medium waveband around
1200kHz.
Good luck
David G0MRF
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