Return-Path: X-Spam-DCC: paranoid 1181; 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=-0.2 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, HTML_40_50,HTML_MESSAGE,RATWARE_GECKO_BUILD 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 u0DGglxD011512 for ; Wed, 13 Jan 2016 17:42:47 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1aJOQo-00076y-E7 for rs_out_1@blacksheep.org; Wed, 13 Jan 2016 16:37:58 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1aJOQn-00076p-V6 for rsgb_lf_group@blacksheep.org; Wed, 13 Jan 2016 16:37:57 +0000 Received: from mailfe02.swip.net ([212.247.154.33] helo=swip.net) by relay1.thorcom.net with esmtp (Exim 4.86) (envelope-from ) id 1aJOPj-0008Dl-Rh for rsgb_lf_group@blacksheep.org; Wed, 13 Jan 2016 16:37:56 +0000 X-T2-Spam-Status: No, hits=0.9 required=5.0 tests=BAYES_50, HTML_MESSAGE Received: from [81.224.101.198] (account cxu-dcw-tyr@tele2.se HELO [192.168.1.7]) by mailfe02.swip.net (CommuniGate Pro SMTP 5.4.4) with ESMTPSA id 645534066 for rsgb_lf_group@blacksheep.org; Wed, 13 Jan 2016 17:36:31 +0100 To: rsgb_lf_group@blacksheep.org References: <1523b989d9e-5764-7820@webprd-a106.mail.aol.com> From: Johan Bodin Message-ID: <56967D14.5090706@tele2.se> Date: Wed, 13 Jan 2016 17:36:36 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <1523b989d9e-5764-7820@webprd-a106.mail.aol.com> X-HELO-Warning: Remote host 212.247.154.33 (mailfe02.swip.net) used invalid HELO/EHLO swip.net - verification failed X-Scan-Signature: 3efbf4053c1a70bbeb6c0a0cc657f05e Subject: Re: LF: Decca 5501 Content-Type: multipart/alternative; boundary="------------080506060609060100020205" 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 10.1.3.10 Status: O X-Status: X-Keywords: X-UID: 6302 This is a multi-part message in MIME format. --------------080506060609060100020205 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Yes, D7 will charge C8 when drive is present, and the time constant of C8, R15, R16 and RV3 is about a millisecond, so IC1b is most likely a drive supervisor. The 29T winding together with D11 clamps the flyback pulse to the +27V rail when the stored magnetic energy is "discharged". This is a quite common method used to make the drain/collector of a single-ended switcher swing symmetrically around around the +V rail. The 27T / 29T difference was probably choosen because of non-perfect coupling and perhaps also the forward drop of D11. I think the zener D28 is there to "eat" the energy in the narrow flyback drain spikes kicking back from the leakage inductance of the 27T primary. I'm not sure about the reason for moving the clamp from +27V to GND (via D10/TR1) when drive is lost. Maybe the transformer is big enough to have plenty of energy storage margin and the final "discharge" is routed through TR1 to GND instead of causing a looong final pulse to the PA FETs? 73 de Johan SM6LKM gw8glo@aol.co.uk wrote: > OK thanks Andy I do have the circuit diagrams but I understood that > the clamp only operated if the drive was lost. The description was not > that clear to me but a probe with the scope may clear that up. I have > added resistors across the fet gates so that if the transformer fails > the fet should turn off. I think I was lucky when the transformer > failed and the fet was not killed! The insulation in the transformer > is only what is on the litz wire and it has sleeving out of the coil. > It failed as the ferrite is earthed and it had degraded the insulation > over time. It was a pig to wind but was worth it, no spares are > probably available unless from a scrap unit. > Dave > > > > -----Original Message----- > From: Andy Talbot > To: rsgb_lf_group > Sent: Wed, 13 Jan 2016 10:45 > Subject: Re: LF: Decca 5501 > > I've just looked again, and there's more to to the drive circuitry > than that. It is single ended drive for current into the inductor, as > I stated, but there is another IRF520 used as an active clamp (the > circuit diagram was drawn a bit ambiguously, so didn't spot the > arrangement straightaway). So when these two FETs are driven > alternately there will be a proper equal amplitude symmetrical drive > waveform generated. > > It is definitely used as an energy storage inductor though, hence a > gapped core is essential. > > 'jnt --------------080506060609060100020205 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit Yes, D7 will charge C8 when drive is present, and the time constant of C8, R15, R16 and RV3 is about a millisecond, so IC1b is most likely a drive supervisor.

The 29T winding together with D11 clamps the flyback pulse to the +27V rail when the stored magnetic energy is "discharged". This is a quite common method used to make the drain/collector of a single-ended switcher swing symmetrically around around the +V rail. The 27T / 29T difference was probably choosen because of non-perfect coupling and perhaps also the forward drop of D11. I think the zener D28 is there to "eat" the energy in the narrow flyback drain spikes kicking back from the leakage inductance of the 27T primary.

I'm not sure about the reason for moving the clamp from +27V to GND (via D10/TR1) when drive is lost. Maybe the transformer is big enough to have plenty of energy storage margin and the final "discharge" is routed through TR1 to GND instead of causing a looong final pulse to the PA FETs?

73 de Johan SM6LKM

gw8glo@aol.co.uk wrote:
OK thanks Andy I do have the circuit diagrams but I understood that the clamp only operated if the drive was lost. The description was not that clear to me but a probe with the scope may clear that up. I have added resistors across the fet gates  so that if the transformer fails the fet should turn off. I think I was lucky when the transformer failed and the fet was not  killed! The insulation in the transformer is only what is on the litz wire and it has sleeving out of the coil. It failed as the ferrite is earthed and it had degraded the insulation over time. It was a pig to wind but was worth it, no spares are probably available unless from a scrap unit.
Dave



-----Original Message-----
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Sent: Wed, 13 Jan 2016 10:45
Subject: Re: LF: Decca 5501

I've just looked again, and there's more to to the drive circuitry than that.  It is single ended drive for current into the inductor, as I stated, but there is another IRF520 used as an active clamp (the circuit diagram was drawn a bit ambiguously, so didn't spot the arrangement straightaway).  So when these two FETs are driven alternately there will be a proper equal amplitude symmetrical drive waveform generated.

It is definitely used as an energy storage inductor though, hence a gapped core is essential. 

'jnt 
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