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Hello Mal an all LF,
I have built an Class-E 100W amp for 136kHz at
approx 85%-90% efficiency at 12VDC with two IRF fet's parallel some time ago.
The capacitors used in the output circuit were somwhat large to transform the
low impedance at the FET output towards the aearial output socket at
50Ohms. For DC separation an elco 450uF at 105degC (normally used in switching
PSU's) worked ok. The PI filter capacitors high voltage type worked fine
(did not get hot). PI filter L is 10uH air wound with a ferrid rod partly
inside moving back/forward inside the coil for tuning the amp at exactly
class-E phase shift and compensating the aereal impedance, not beeing exactly 50
ohms in practice of course. Any iron near the coil melts! so use only
copper/brass materials there.
The first pair of fets have been blown up by not
switching the gate fully in voltage. No fet will survive if DS is not turned
fully open instantly. Normal DS resistance at Vgate > 2V is below
0.3Ohm, power dissipated within fet specs at class-E. At Vgate below 2V
the Pds=Vds*Ids at the phase shift that works for class E will destroy
any fet. Sloppy gate switching / driving the class-E wit a sine-wave
and you're up for trouble sooner or later (aereal 50Ohm
mismatch).
Kind regards, best 73's,
Mike, PC4M
----- Original Message -----
Sent: Thursday, November 26, 2009 11:40
AM
Subject: LF: CLASS E
MF and Co
Getting suitable capacitors is the problem, not
normally available from the junk box.
Maybe a class F amp is the answer or the
mechanical G turbo charged rumoured to be over 100%
efficient
G3KEV
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