Return-Path: Received: (qmail 29056 invoked from network); 21 Jan 2004 01:35:24 -0000 Received: from unknown (HELO ptb-mxscan02.plus.net) (212.159.14.236) by ptb-mailstore02.plus.net with SMTP; 21 Jan 2004 01:35:24 -0000 Received: (qmail 94335 invoked from network); 21 Jan 2004 01:35:23 -0000 X-Filtered-by: Plusnet (hmail v1.01) X-Spam-detection-level: 11 Received: from ptb-mxcore02.plus.net (212.159.14.216) by ptb-mxscan02.plus.net with SMTP; 21 Jan 2004 01:35:22 -0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore02.plus.net with esmtp (Exim) id 1Aj7H8-000OQN-KT for dave@picks.force9.co.uk; Wed, 21 Jan 2004 01:35:22 +0000 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Aj7Ge-0001tK-U7 for rs_out@blacksheep.org; Wed, 21 Jan 2004 01:34:52 +0000 Received: from [194.73.73.93] (helo=rhenium.btinternet.com) by post.thorcom.com with esmtp (Exim 4.14) id 1Aj7Ge-0001tB-By for rsgb_lf_group@blacksheep.org; Wed, 21 Jan 2004 01:34:52 +0000 Received: from [213.122.58.240] (helo=Main) by rhenium.btinternet.com with smtp (Exim 3.22 #25) id 1Aj7Gd-0000y5-00 for rsgb_lf_group@blacksheep.org; Wed, 21 Jan 2004 01:34:51 +0000 X-Bad-Message-ID: no DNS (Main) Message-ID: <001301c3dfbe$cc459b80$6507a8c0@Main> From: "Alan Melia" To: "LF-Group" Date: Wed, 21 Jan 2004 01:35:01 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4522.1200 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Subject: LF: re TC44 etc Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.60 (1.212-2003-09-23-exp) on post.thorcom.com X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.60 X-SA-Exim-Scanned: Yes Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SPAMFiltered: yes X-Spam-Rating: 2 Hi Dick, it is not really all that necessary to use that chip. It is quite possible to drive the gates quite adequately with a PNP-NPN totem pair (emitter followers...the emitters to the output ...npn top pnp bottom...bases strapped together). These can be driven from 12v logic levels (cmos) Most switching FETs will turn on at about 6 volts but need around 10 to 12 volts for high currents. In fact the chipp can be a cause of FET failure, it you remove the drive from the TC44xx and dont kill the supply the output just stays high, holding the FET on. I think there are some advantages in the keying technique used by Dave G3YXM and Dave G0MRF, in that as the supply is keyed the "ON" times changes "gently" helping tame the click. Cheers de Alan G3NYK alan.melia@btinternet.com