Envelope-to: dave@picks.force9.co.uk Delivery-date: Wed, 28 Sep 2005 16:21:21 +0100 Received: by ptb-mxcore16.plus.net with spam-scanned (PlusNet MXCore v2.00) id 1EKdkG-0001oq-SK for dave@picks.force9.co.uk; Wed, 28 Sep 2005 16:21:21 +0100 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore16.plus.net with esmtp (PlusNet MXCore v2.00) id 1EKdkG-0001oR-IA for dave@picks.force9.co.uk; Wed, 28 Sep 2005 16:21:20 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1EKdjd-00062F-ER for rs_out_1@blacksheep.org; Wed, 28 Sep 2005 16:20:41 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1EKdjd-000626-2L for rsgb_lf_group@blacksheep.org; Wed, 28 Sep 2005 16:20:41 +0100 Received: from newbox.tcp.net.uk ([195.80.0.243]) by relay1.thorcom.net with esmtp (Exim 4.51) id 1EKeID-0001eT-Px for rsgb_lf_group@blacksheep.org; Wed, 28 Sep 2005 16:56:31 +0100 Received: from standalone ([212.248.140.7]) by newbox.tcp.net.uk (8.12.7/8.12.7) with SMTP id j8SFL39a020181 for ; Wed, 28 Sep 2005 16:21:03 +0100 (BST) Message-ID: <001601c5c43f$be1b6fa0$078cf8d4@standalone> From: "Andy" To: rsgb_lf_group@blacksheep.org Date: Wed, 28 Sep 2005 16:17:27 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 4.72.3110.5 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 X-TCP-MailScanner-Information: Please visit www.tcp.co.uk for more information X-TCP-MailScanner: Found to be clean X-TCP-MailScanner-From: actalbot@southsurf.com Subject: LF: Re: Re: RE: Re: Advice will be gratefully received Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit 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-PN-SpamFiltered: by PlusNet MXCore (v2.00) My 700W design used 500V IRF462 devices in half bridge running from a 340V rail - not a massive design margin there. I used transformer drive direct to the devices, with the transformer primary driven from a TC4426 IC running from +15V rail (via a capacitor of course!). The drive transformer turns ratio was 1:1+1 so the FETs received 15V drive peak-peak. I did wonder, initially, about the need for negative gate clamps, but there was no reason to do so at all for any reasons associated with MOSFET itself. Switch Mode PSUs need DC restoration after a drive transformer because they don't use a 1:1 duty cycle, but that is not the case here; duty cycle is exactly 50%. That 700W Tx copied the Decca idea of having a small damped inductor in series with the two FETs to absorb with the switching transient. I blew many devices during the development phase, but all explosions were accounted for and the design is very robust now. Andy G4JNT/G8IMR -----Original Message----- From: Alan Melia To: rsgb_lf_group@blacksheep.org Date: 2005/09/28 13:54 Subject: LF: Re: RE: Re: Advice will be gratefully received >Negative drive swing clamps.....I think I am right in that.... check in the >Decca circuit (LF Exp Hdbk) that is transformer driven. >My guess is the 100V devices will just stand the 24 volt supply >Cheers de Alan > >----- Original Message ----- >From: "OSBORN, Chris" >To: >Sent: 28 September 2005 12:01 >Subject: LF: RE: Re: Advice will be gratefully received > >