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Date: Thu, 9 Aug 2012 11:08:55 +1000
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From: Dimitrios Tsifakis <dtsifakis@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Caps for Class-E amp
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>> Output impedance is about 1.4 ohm. I have designed it to produce 50 W
>> at 12 V and of course 200 W at 24V.
>
> Yes, good idea. In /p for moderate power and at home in QRO :-)

That's exactly the idea :-) Also, if all components are selectedfor a
QRO operation, they will probably survive any kind of dodgy condition
you may encounter in the field.

>>   I work in multiples of 12 V as I
>> normally use big SLA batteries to power my equipment. The FET is a
>> monster IXYS 500V/55A FET which should be bombproof.
>
> But you could have much lower on-resistances when using a 100V FET. 200W at
> 24V is no problem though. IXYS is mostly a good choice. But quite expensive.
> Once you lost a pair of them you begin to think to go back to the IRFP
> types, at least i have done so ;-)

I did not buy that FET, I was given it by a friend who bought it for a
project but ended up not using it. The Rds(on) is 0.09 ohm, which is
not that bad. Higher Rds(on) will result in a bit more heat on the
heat sink and slightly less power for the same supply voltage, but no
other serious side effect. The biggest problem with using a monster
FET is the Ciss which is about 10 nF. This makes it a bit more
difficult to drive than other smaller FETs, even at 137 kHz. But I
found that the TC4420 (6 A peak) FET driver that I had in my junk box,
seems to be happy with that Ciss/frequency combination.

73, Dimitris VK1SV