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=-2.0 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, HTML_30_40,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 t7ADVt2N024474 for ; Mon, 10 Aug 2015 15:31:55 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ZOn6V-0004WE-Hw for rs_out_1@blacksheep.org; Mon, 10 Aug 2015 14:27:03 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ZOn6V-0004W5-5m for rsgb_lf_group@blacksheep.org; Mon, 10 Aug 2015 14:27:03 +0100 Received: from mail-wi0-f181.google.com ([209.85.212.181]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.86) (envelope-from ) id 1ZOn5R-00029r-0I for rsgb_lf_group@blacksheep.org; Mon, 10 Aug 2015 14:27:02 +0100 Received: by wicne3 with SMTP id ne3so135909578wic.1 for ; Mon, 10 Aug 2015 06:25:40 -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=sG3Ui5LZK8SfJYaTRFSb0xBbc8pLncYxZjlkY8muP1g=; b=fRUJ5jSCiQrwISD3Y1+NDPqsjIymQRsaE8+G3cfO5YasECllrbn8fdwph9TF8OWvxd tothymYc/7cK2wos+rmlJFVeUHAWP4o6oc+Jd3oHqCHp126GHJZHT16ec/JsgXUYJeUF QJDoLAUsZ7KKWbTEcAxrnfcR0KvSmyUc2I1BHzUm1pevFnKjs0NT5MBuXYFAS0/OwwzK JZTTx39LjLpi4lNKTCuPnQiEr5KcUD3VfbdZ0kFmdGs9mBYC9oLVTRhWwE2J4Uf9jR3U qZduXDpcHkz75/4jMFtYgHTF6H9E4hoRxTEhNdB4JELbf0/lYaaVDovFPT0jHtVN8u4q Vy+A== MIME-Version: 1.0 X-Received: by 10.194.86.161 with SMTP id q1mr45679679wjz.18.1439213140731; Mon, 10 Aug 2015 06:25:40 -0700 (PDT) Received: by 10.28.98.6 with HTTP; Mon, 10 Aug 2015 06:25:40 -0700 (PDT) In-Reply-To: References: <1892164761.20150810130954@chriswilson.tv> Date: Mon, 10 Aug 2015 14:25:40 +0100 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org X-Scan-Signature: 617a5faed955112e448650f4d003a84d Subject: Re: LF: Protecting a MOSFET driver chip from MOSFET failure? Content-Type: multipart/alternative; boundary=089e0102ff7a026c38051cf4ecb7 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: 3842 --089e0102ff7a026c38051cf4ecb7 Content-Type: text/plain; charset=UTF-8 Forgot to mention, although I hope it is more than self-evident to readers here, the diode is orientated so it points 'upwards'; allowing a positive drive voltage to appear on the gate and clamping the negative to ground. Andy G4JNT On 10 August 2015 at 13:31, Andy Talbot wrote: > 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 >> >> >> > --089e0102ff7a026c38051cf4ecb7 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Forgot to mention, although I hope it is more than self-ev= ident to readers here, the diode is orientated so it points 'upwards= 9;; =C2=A0allowing a positive drive voltage to appear on the gate and clamp= ing the negative =C2=A0to ground.

Andy =C2=A0G4JNT
=

On 10 August 2015= at 13:31, Andy Talbot <andy.g4jnt@gmail.com> wrote:
<= blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px= #ccc solid;padding-left:1ex">
Yes there is.=C2=A0 Or , are= : several.

Don't drive the MOSFET directly from the IC.=C2= =A0 Instead use a capacitor and DC restorer circuit.=C2=A0 That guards agai= nst both =C2=A0the 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 li= ke IN914 , 1N4148 etc from gate to ground.=C2=A0 Shunt the diode with a res= istor of a few kohms to stop it floating

The capac= itor decouples the chip output at DC.=C2=A0 The diode clamps the waveform a= t the cap output / gate so it's most negative excursion is forced to si= t near enough at ground.

Or use transformer coupli= ng, as in my QRO 137kHz transmitter. =C2=A0http://www.g4jnt.com/137tx.pdf
<= br>
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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