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Message-ID: <001001c83c1d$38af7480$0900a8c0@Lark>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <001201c83be4$79fff920$0401a8c0@ken> <001f01c83be6$6978cb20$0900a8c0@Lark> <001a01c83be8$4be13140$0401a8c0@ken>
Date: Tue, 11 Dec 2007 17:40:04 -0000
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Subject: LF: Re: RE: Re: IRF530N in 500kHz PA
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Hi Ken then you may need either a transformer or a switching stage that will
drive move that 6 to 8 volts on to the gate and handle the high gate
capacitance. There is not much point I believe in trying to run in Class C
with this kind of device, It is a lot easier to go right to Class D/E, they
are not very linear devices. You may get nearer to Class C type operation
with a audio power FET but these are much more expensive. The 530 is
intended to be used as a switch.

The step up output circuit does work I have used one of these on a PA stage.
It does need tuning which is a little difficult (high C) but does avoid a
transformer. You do also need to be careful about the coils. I uses low
permiability iron dust or air cored. Ferrite cores are too lossy in this
application (filters and tuned circuits).

Good Luck with it
Cheeers de Alan G3NYK


----- Original Message -----
From: "Ken Wright" <ken.h.wright@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, December 11, 2007 11:23 AM
Subject: LF: RE: Re: IRF530N in 500kHz PA


Hi Alan, Thanks for the reply, I am trying to run it in pseudo class C,
driving it from a xtal controlled osc, 10mW output into a buffer/driver amp.

 73 Ken M0KHW

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Alan Melia
Sent: 11 December 2007 11:10
To: rsgb_lf_group@blacksheep.org
Subject: LF: Re: IRF530N in 500kHz PA

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