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=-2.4 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, HTML_MESSAGE 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 t7ACZmf0024301 for ; Mon, 10 Aug 2015 14:35:48 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ZOmFu-000488-UK for rs_out_1@blacksheep.org; Mon, 10 Aug 2015 13:32:42 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ZOmFu-00047z-J8 for rsgb_lf_group@blacksheep.org; Mon, 10 Aug 2015 13:32:42 +0100 Received: from mail-wi0-f178.google.com ([209.85.212.178]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.86) (envelope-from ) id 1ZOmEq-0001w8-9o for rsgb_lf_group@blacksheep.org; Mon, 10 Aug 2015 13:32:41 +0100 Received: by wibhh20 with SMTP id hh20so148539787wib.0 for ; Mon, 10 Aug 2015 05:31:22 -0700 (PDT) X-DKIM-Result: Domain=gmail.com Result=Good and Known Domain DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=VOYQTV48dO89sYoLBAeaRjOxmQ9CZe8EPeNJh5zgdH8=; b=wq0L7NCbQdudpnF/VMIjqRYz2L6puJSbY1uzAYzWdbsB90D/o71iXBmGGZXCRw5ITn UDiptuNKglR/Ssr8Gq7dtJOcImt9t1AFfvaeDT/LpdyWRpqaUu4PRWbtpFH24FMvgzyt NvAnpVqEqjTYhzc8NlHiIZDl1RoxWCZf8J1LWFn7QYFNc1orAX41Npfv2vb3SEVIxTkP k95ch8D7aq33UeP0txbn/HvN1S7dWDp/tlLPaLzbuXBgvSzg8EOB3c3IKA2XEi+g1dJG vO7dxsRCdUR2F2JMQ6OWPSpmYovKnPhSu/LyFZu6SjaLCA6uosmPArh+ZSkb290SjIE8 deUA== MIME-Version: 1.0 X-Received: by 10.180.73.2 with SMTP id h2mr24817280wiv.72.1439209882143; Mon, 10 Aug 2015 05:31:22 -0700 (PDT) Received: by 10.28.98.6 with HTTP; Mon, 10 Aug 2015 05:31:22 -0700 (PDT) In-Reply-To: <1892164761.20150810130954@chriswilson.tv> References: <1892164761.20150810130954@chriswilson.tv> Date: Mon, 10 Aug 2015 13:31:22 +0100 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org X-Scan-Signature: 54c274b8b0f8da777e8f702c98fe24ad Subject: Re: LF: Protecting a MOSFET driver chip from MOSFET failure? Content-Type: multipart/alternative; boundary=f46d043be0eac84fab051cf4297c 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: 3839 --f46d043be0eac84fab051cf4297c Content-Type: text/plain; charset=UTF-8 Yes there is. Or , are: several. Don't drive the MOSFET directly from the IC. Instead use a capacitor and DC restorer circuit. That guards against both the driver staying high permanently if drive is removed, and also against IC damage if the FET fails Capacitor (typically 100nF for 137/475kHz) from IC output to gate Diode like IN914 , 1N4148 etc from gate to ground. Shunt the diode with a resistor of a few kohms to stop it floating The capacitor decouples the chip output at DC. The diode clamps the waveform at the cap output / gate so it's most negative excursion is forced to sit near enough at ground. Or use transformer coupling, as in my QRO 137kHz transmitter. http://www.g4jnt.com/137tx.pdf Andy G4JNT On 10 August 2015 at 13:09, Chris Wilson wrote: > 10 August 2015 > > > Is there a way of protecting a typical MOSFET driver IC from being > taken out by a MOSFET failure in a Class E LF amp? > > I was experimenting with drive level into my G3YXM 1kW 136 kHz amp and > managed to blow 2 of the 4 IRFP450 MOSFET's and half the TC4426 driver > chip. > > I also came to realize that I did not follow my car engineering > knowledge, and built the thing with little regard to servicing it, > changing the devices was surgically challenging (read a PITA...) and I > should perhaps have put them on PCB screw type connector blocks in a > more accessible position. If I build another that would be my main > change, making repair access far easier! > > > As an aside why would reducing drive to the amp perhaps cause MOSFET > failure when TX'ing into a dummy load? > > > I am still trying to find a way to set the over current trip on this, > it's by means of a Hall effect sensor looking at the south pole of the > ferrite choke CH1. The thing draws 12.5 amps tops when TX'ing into a > dummy load, and even with the Hall sensor against the face of the > ferrite (and I am sure I have the south pole end, and the correct face > of the Hall sensor together), it doesn't trip, diagram at > http://www.chriswilson.tv/schematic_modified_2.jpg > > Am I going to have to put some stonking big resistor on the output end > of the choke and try and make it draw more current momentarily? > > Thanks, and thanks for a most entertaining "LF Weekend" sadly I was > not able to get an antenna sorted in time. > > > > > -- > > > Best regards, > Chris mailto:chris@chriswilson.tv > > > --f46d043be0eac84fab051cf4297c Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Yes there is.=C2=A0 Or , are: several.

Don= 9;t drive the MOSFET directly from the IC.=C2=A0 Instead use a capacitor an= d DC restorer circuit.=C2=A0 That guards against both =C2=A0the driver stay= ing high permanently if drive is removed, and also against IC damage if the= FET fails

Capacitor (typically 100nF for 137/475k= Hz) from IC output to gate
Diode like IN914 , 1N4148 etc from gat= e to ground.=C2=A0 Shunt the diode with a resistor of a few kohms to stop i= t floating

The capacitor decouples the chip output= at DC.=C2=A0 The diode clamps the waveform at the cap output / gate so it&= #39;s most negative excursion is forced to sit near enough at ground.
=

Or use transformer coupling, as in my QRO 137kHz transm= itter. =C2=A0http://www.g4jnt.co= m/137tx.pdf

Andy =C2=A0G4JNT


On= 10 August 2015 at 13:09, Chris Wilson <chris@chriswilson.tv> wrote:
10 August 2015


Is there a way of protecting a typical MOSFET driver IC from being
taken out by a MOSFET failure in a Class E LF amp?

I was experimenting with drive level into my G3YXM 1kW 136 kHz amp and
managed to blow 2 of the 4 IRFP450 MOSFET's and half the TC4426 driver<= br> chip.

I also came to realize that I did not follow my car engineering
knowledge, and built the thing with little regard to servicing it,
changing the devices was surgically challenging (read a PITA...) and I
should perhaps have put them on PCB screw type connector blocks in a
more accessible position. If I build another that would be my main
change, making repair access far easier!


As an aside why would reducing drive to the amp perhaps cause MOSFET
failure when TX'ing into a dummy load?


I am still trying to find a way to set the over current trip on this,
it's by means of a Hall effect sensor looking at the south pole of the<= br> ferrite choke CH1. The thing draws 12.5 amps tops when TX'ing into a dummy load, and even with the Hall sensor against the face of the
ferrite (and I am sure I have the south pole end, and the correct face
of the Hall sensor together), it doesn't trip, diagram at
http://www.chriswilson.tv/schematic_modified_2.jpg=

Am I going to have to put some stonking big resistor on the output end
of the choke and try and make it draw more current momentarily?

Thanks, and thanks for a most entertaining "LF Weekend" sadly I w= as
not able to get an antenna sorted in time.




--


Best regards,
=C2=A0Chris=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 mailto:chris@chriswilson.tv



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