Return-Path: X-Spam-DCC: paranoid 1290; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-0.5 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, FORGED_RCVD_HELO,RATWARE_GECKO_BUILD,SPF_PASS autolearn=no version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id u1SNsqc7004243 for ; Mon, 29 Feb 2016 00:54:52 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1aaB7I-0004hA-4r for rs_out_1@blacksheep.org; Sun, 28 Feb 2016 23:51:12 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1aaB7H-0004h1-Pi for rsgb_lf_group@blacksheep.org; Sun, 28 Feb 2016 23:51:11 +0000 Received: from brian.netcom.co.uk ([217.72.171.64]) by relay1.thorcom.net with esmtp (Exim 4.86) (envelope-from ) id 1aaB5T-0000b6-69 for rsgb_lf_group@blacksheep.org; Sun, 28 Feb 2016 23:51:10 +0000 Received: from sb.abelian.org (i-194-106-52-83.freedom2surf.net [194.106.52.83]) by brian.netcom.co.uk (Postfix) with ESMTP id D67CD18EB83 for ; Sun, 28 Feb 2016 23:26:17 +0000 (GMT) Received: from [127.0.0.1] (localhost [127.0.0.1]) by sb.abelian.org (Postfix) with ESMTP id 4026D28A0227 for ; Sun, 28 Feb 2016 23:48:42 +0000 (UTC) Message-ID: <56D3875A.4060405@abelian.org> Date: Sun, 28 Feb 2016 23:48:42 +0000 From: Paul Nicholson User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130106 Thunderbird/17.0.2 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <56D08BEF.7070708@abelian.org> <8D33ED4DA8562EE-14E0-601004@webmail-vm018.sysops.aol.com> <56D0934B.1040700@abelian.org> <56D098D3.80501@abelian.org> <56D0B22B.2020107@abelian.org> <56D0B58A.80908@tiscali.co.uk> <56D0C373.1090004@abelian.org> <56D0CC55.1060400@tele2.se> <56D0D587.7080309@abelian.org> <56D1DEAF.10202@abelian.org> <56D1FD5F.3010301@abelian.org> <56D2DA6D.20209@tele2.se> <56D326F1.1000102@abelian.org> <56D33297.9080209@abelian.org> <56D37529.9070607@abelian.org> <6732A7AB5E094156B6AE3A33E58A964F@White> In-Reply-To: <6732A7AB5E094156B6AE3A33E58A964F@White> X-Scan-Signature: c8ff00257edaad8e124ab9389da9609a Subject: Re: LF: MF: EbNaut Content-Type: multipart/mixed; boundary="------------010903000704030108080304" 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-Scanned-By: MIMEDefang 2.56 on 10.1.3.11 Status: O X-Status: X-Keywords: X-UID: 7103 This is a multi-part message in MIME format. --------------010903000704030108080304 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Attached a circuit of part of the push-pull PA. The center tap of the primary is at AC ground with the DC supply coming in via a choke. I've been getting a lot of ringing on the drains, as is fairly normal I guess. Even with very low leakage inductance there are large spikes appearing on the drain when the device is off. I took a close look at these spikes and realised they were transients running down the primary and reflecting off the AC grounded mid-point. For example there's a spike 40nS wide occurring 350nS after the FET switches off, then another after a further 350nS, and then a third, each with diminishing amplitude. This is clearly a transient propagating back and forth along the primary. My attempts to suppress this spike with the usual snubber led to some hot resistors but not much attenuation. So over a cup of tea I wondered what would happen if I let the transient go the full distance of the double primary. I removed C1 to let the center float at AC. Now the round trip time of the transient has increased a lot and it's just arriving back at the drain when the FET switches back on again. Result: no transient. An unexpected side effect is that the transformer windings are now cool. I'm not quite sure how the circuit is working without an AC ground through C1 but the efficiency has improved. Has anyone else had trouble with such primary transients? On the scope they look quite different to the decaying sinusoid of leakage inductance ringing with drain capacitance, they appear as a succession of spikes with long intervals between. -- Paul Nicholson -- --------------010903000704030108080304 Content-Type: image/gif; name="pa.gif" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="pa.gif" R0lGODdhnwFFAfcAAAAAAAEBAQoKChERERMTExcXFx0dHSIiIiYmJjMzMzk5OURERFVVVWZm ZnJycnd3d39/f4iIiJmZmaqqqru7u8zMzN3d3e7u7v///wA8AWCEAAQIAAgABIgQAMsAAL8A AJNzAXTHAGxIALe3ADw8AISEAAgIADAwAEUkAABiAAC3AAAwAOkkABhiAAi3APT0mB8fpHxK j7e3CAgBazAAsoQADggACPRo9B+DD3xYYre3twj0mDAfpIRKjwi3CAq3AHVtAGxsAAhgWDA8 iISEywgIvwH09ABMDwCEYgAItwDEmACGpADLjwC/CErICgKGT2DLUAS/twDk9ACOD/SgAx+G UHzLULe/twDsmABMpACEjwAICMHG4G/ByWpIFwgAayP0AQIfAGB8AAS3AErAIAICCWAAYgQA t1Sk9A7AD2xIYghg4DA8yYSEFwgICADYbwCGAABYYAC3BAD0WwAfUABKUAC3t6j04IgfyctK F7+3CAD0awAfsgBKDgC3CG/YAWBYAFj0YIgfMIP04cwf0AdKB1Bg4GU8yYmEF5/YawGGsgBY 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