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From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <001201c83be4$79fff920$0401a8c0@ken>
Date: Tue, 11 Dec 2007 11:10:14 -0000
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Subject: LF: Re: IRF530N in 500kHz PA
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Hi Ken I suggest you are probably not driving it hard enough. Many of these
switching FETs require more than 6 volts to swich on hard and they have a
very high gate capacity so you need some current drive capability as well.
We have used a pnp-npn totem pole driver on 12v to good effect. I think
there may be troubles if you are trying to get it linear. If you are trying
to go ClassD/ E then you should not be tuning for max output but for the
correct drain wave form. I cant comment on Class A /B performance.

http://www.alan.melia.btinternet.co.uk/classepa.htm

Cheers de Alan G3NYK


----- Original Message -----
From: "Ken Wright" <ken.h.wright@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, December 11, 2007 10:56 AM
Subject: LF: IRF530N in 500kHz PA


Has anyone experienced problems using an IRF530N in a 500kHz PA?. I am using
an IRF530N into an L – C – L  output network the design parameters for the
network are input:10 ohms, output 50 ohms, centre frequency 502.5 kHz, Q =
12, giving, L1  38µH, C1 3.7nF, L2  84µH, C1 consists of a 3.3nF fixed
capacitor plus a 2 gang 500pF variable, 3mH inductor in the drain. I have
tried driving the MOSFET with a 5v positive peak signal, and with a 3v rms
signal sitting on a +ve bias, I have managed to obtain 5w into a Marconi
TF1152A/1 (50Ω) power meter about three times, but when 12v is removed from
the PA and reconnected there is no output, C1 is adjusted for maximum power
output, but is never the same position twice, and there seems to be a very
critical adjustment of the drive to obtain, a) an output, b) anything that
looks like a sine wave, although when I have got it right there is a very
good sine wave. Any ideas anyone as to what may be going wrong?



My direct e-mail is  ken.h.wright@btinternet.com





73   Ken Wright   M0KHW    IO91TV