Return-Path: Received: (qmail 30979 invoked from network); 18 Jul 2004 06:43:16 -0000 Received: from unknown (HELO ptb-spamcore02.plus.net) (192.168.71.3) by ptb-mailstore02.plus.net with SMTP; 18 Jul 2004 06:43:16 -0000 Received: from mailnull by ptb-spamcore02.plus.net with spamcore-l-b (Exim 4.32; FreeBSD) id 1Bm5Q3-00027y-9x for dave@picks.force9.co.uk; Sun, 18 Jul 2004 07:45:07 +0100 Received: from [192.168.67.2] (helo=ptb-mxcore02.plus.net) by ptb-spamcore02.plus.net with esmtp (Exim 4.32; FreeBSD) id 1Bm5Q3-00027m-7p for dave@picks.force9.co.uk; Sun, 18 Jul 2004 07:45:07 +0100 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore02.plus.net with esmtp (Exim) id 1Bm5OE-000JGD-GO for dave@picks.force9.co.uk; Sun, 18 Jul 2004 06:43:14 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Bm5Nx-0003u9-Br for rs_out_1@blacksheep.org; Sun, 18 Jul 2004 07:42:57 +0100 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Bm5Nw-0003ty-UV for rsgb_lf_group@blacksheep.org; Sun, 18 Jul 2004 07:42:56 +0100 Received: from mail.genesiswireless.com ([63.171.43.8] helo=ms.genesis-technology.com) by relay.thorcom.net with esmtp (Exim 4.34) id 1Bm5Nt-0001L0-9R for rsgb_lf_group@blacksheep.org; Sun, 18 Jul 2004 07:42:56 +0100 Received: from genesiswireless.us (rev-65.165.20.192.genesiswireless.us [65.165.20.192]) by ms.genesis-technology.com (8.12.9/8.12.9) with ESMTP id i6I6fYVO011975 for ; Sun, 18 Jul 2004 01:41:35 -0500 Message-ID: <40FA1C54.7050304@genesiswireless.us> Date: Sun, 18 Jul 2004 01:44:36 -0500 From: WE0H Mike User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <30.5b6a360a.2e2b7415@aol.com> In-Reply-To: <30.5b6a360a.2e2b7415@aol.com> X-Scanned-By: MIMEDefang 2.36 X-Spam-Score: 2.1 (++) X-Spam-Report: autolearn=no,HTML_20_30=0.474,HTML_MESSAGE=0.001,HTML_TITLE_EMPTY=0.544,MAILTO_TO_SPAM_ADDR=1.052 Subject: Re: LF: clicking matching transformer... Content-Type: text/html; charset=windows-1252 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: ** X-Spam-Status: No, hits=2.1 required=5.0 tests=HTML_20_30,HTML_MESSAGE, HTML_TITLE_EMPTY,MAILTO_TO_SPAM_ADDR autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Spam-Filtered: by PlusNet SpamCORE (v3.00) Content-transfer-encoding: 8bit Hi David,
What would you recommend for a supply voltage with 500v FET's in your Quarter Kilowatt linear amp design?

Mike
WE0H
WD2XGI

G0MRF@aol.com wrote:

In a message dated 17/07/2004 20:32:33 GMT Standard Time, sthed475@telus.net writes:

Any thoughts on if a matching transformer should 'click' when the key is released... Obviously it is likely an inductive reaction to the rapid change in current supplied... When I connect the 48V supply to the system the finals don't last long... OK at 12 and 24V so I feel it is a inductive kickback that's blasting the 200V rated FETs... The system works great into a 6 ohm load driver pushpull without the match xfmr... It must be the inductive kickback...

Perhaps the inductance of the windings it too great?

Damn physics... To quote a power engineer friend of mine "it's a damn shame that FETs behave the way they do, otherwise they would be the perfect device..."

200V FETs probably are being hit by some fairly high voltages. I have seen 200V spikes from a 35V supply line, particually when the load impedance is incorrect.

On one TX here that operates from a 48 - 56V SMPSU, I had to fit 400V FETs. That solved the problem and gave 600W output. Other choice is to to fit 200V 'transorbs' (?) across the devices. If the spikes are narrow this may be OK. If not, it's only one more thing to catch fire (hi)

73

David G0MRF