In a message dated 1/11/2004 12:30:03 PM Eastern Standard Time,
[email protected] writes:
nonconducting side. Eather a steady current and heat on the
FET's or by
adding a cap from D to G.
This may be a mistake, but please remember you may have peaks to 200V on the
drains and a limit of 20V (ish) on the gates. Any capacitor as suggested will
destroy the devices in an instant.
I have seen a few 'mods' including a zobel network i.e. a capacitor and resistor in series between drain and ground. This does de-Q the circuit quite well. Changes in value of the normal drain to ground 10nF will have some effect but it's likely to change any resonant frequency without reducing the Q or the total peak voltage. Bob G8RW ran his unit at over 300W and had installed 'transorbs' that conducted just below the max drain limit of the FETs. However, Bob's just had a single peak at the switch on / off points and not the 'ringing' described here. It may be worth looking at the T94-2 core / decoupling caps as well if ringing is at 1MHz+
73
David G0MRF
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