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=-2.1 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, FORGED_RCVD_HELO,HTML_50_60,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 t7AEftZk025036 for ; Mon, 10 Aug 2015 16:41:55 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ZOoBf-0004np-Nb for rs_out_1@blacksheep.org; Mon, 10 Aug 2015 15:36:27 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ZOoBf-0004ng-B1 for rsgb_lf_group@blacksheep.org; Mon, 10 Aug 2015 15:36:27 +0100 Received: from rhcavuit02.kulnet.kuleuven.be ([134.58.240.130] helo=cavuit02.kulnet.kuleuven.be) by relay1.thorcom.net with esmtp (Exim 4.86) (envelope-from ) id 1ZOoAe-0002PF-6L for rsgb_lf_group@blacksheep.org; Mon, 10 Aug 2015 15:36:26 +0100 X-KULeuven-Envelope-From: rik.strobbe@fys.kuleuven.be X-KULeuven-Scanned: Found to be clean X-KULeuven-ID: 408A312834A.A2641 X-KULeuven-Information: Katholieke Universiteit Leuven Received: from icts-p-smtps-1.cc.kuleuven.be (icts-p-smtps-1e.kulnet.kuleuven.be [134.58.240.33]) by cavuit02.kulnet.kuleuven.be (Postfix) with ESMTP id 408A312834A for ; Mon, 10 Aug 2015 16:35:02 +0200 (CEST) Received: from ICTS-S-HUB1.luna.kuleuven.be (icts-s-hub1.luna.kuleuven.be [10.112.9.15]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) by icts-p-smtps-1.cc.kuleuven.be (Postfix) with ESMTPS id 3E3AA40A8 for ; Mon, 10 Aug 2015 16:35:02 +0200 (CEST) Received: from ICTS-S-MBX1.luna.kuleuven.be ([fe80::edaf:341f:90e:f70e]) by ICTS-S-HUB1.luna.kuleuven.be ([fe80::f5f7:d8cc:bee0:28d3%26]) with mapi id 14.03.0224.002; Mon, 10 Aug 2015 16:35:01 +0200 X-Kuleuven: This mail passed the K.U.Leuven mailcluster From: Rik Strobbe To: "rsgb_lf_group@blacksheep.org" Thread-Topic: LF: Protecting a MOSFET driver chip from MOSFET failure? Thread-Index: AQHQ02YORbNs1rM0g0Kx5rSsP5rsAJ4FCJoAgAAPLACAADKnOIAAAkb5 Date: Mon, 10 Aug 2015 14:35:01 +0000 Message-ID: <7E7DFBB4D102A04DB5ADC88D66628A4A443E0BC1@ICTS-S-MBX1.luna.kuleuven.be> References: <1892164761.20150810130954@chriswilson.tv> , In-Reply-To: Accept-Language: nl-BE, en-GB, en-US Content-Language: nl-BE X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mimectl: Produced By Microsoft Exchange V14.3.123.2 x-originating-ip: [10.112.13.12] MIME-Version: 1.0 X-HELO-Warning: Remote host 134.58.240.130 (rhcavuit02.kulnet.kuleuven.be) used invalid HELO/EHLO cavuit02.kulnet.kuleuven.be - verification failed X-Scan-Signature: 14522a7d8bfffcae5e92e35059f18ae1 Subject: RE: LF: Protecting a MOSFET driver chip from MOSFET failure? Content-Type: multipart/alternative; boundary="_000_7E7DFBB4D102A04DB5ADC88D66628A4A443E0BC1ICTSSMBX1lunaku_" 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: 3844 --_000_7E7DFBB4D102A04DB5ADC88D66628A4A443E0BC1ICTSSMBX1lunaku_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Maybe also worth to mention: Capacitive coupling of the driver to the gate= will reduce the peak voltage at the gate by half (assuming 50% duty cycle)= . The IC driver voltage should be at least 12V in order to ensure proper swit= ching of the MOSFET. If you use a transformer (as suggested by Stefan) one can fiddle with the t= ransformer ratio to get the proper voltage at the gate. 73, Rik ON7YD - OR7T ________________________________ Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org= ] namens Andy Talbot [andy.g4jnt@gmail.com] Verzonden: maandag 10 augustus 2015 15:25 Aan: rsgb_lf_group@blacksheep.org Onderwerp: Re: LF: Protecting a MOSFET driver chip from MOSFET failure? 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 D= C restorer circuit. That guards against both the driver staying high perm= anently 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 wavefo= rm at the cap output / gate so it's most negative excursion is forced to si= t near enough at ground. Or use transformer coupling, as in my QRO 137kHz transmitter. http://www.g= 4jnt.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 --_000_7E7DFBB4D102A04DB5ADC88D66628A4A443E0BC1ICTSSMBX1lunaku_ Content-Type: text/html; charset="iso-8859-1" Content-ID: <1FD4914EA684244185674885760AC19B@luna.kuleuven.be> Content-Transfer-Encoding: quoted-printable

Maybe also w= orth to mention: &nb= sp;Capacitive coupling of the driver to the gate will reduce the peak voltage at the gate by half (assuming 50% duty cycle).

The IC driver voltage should be = at least 12V in order to ensure proper switching of the MOSFET.

If you use a transformer (as&nbs= p;suggested by Stefa= n) one can = ;fiddle with the transformer ratio to get the proper voltage at the gate.

 

73, Rik &nbs= p;ON7YD - OR7T

 

Van: owner-rsgb_lf_group@blacksheep.org [o= wner-rsgb_lf_group@blacksheep.org] namens Andy Talbot [andy.g4jnt@gmail.com= ]
Verzonden: maandag 10 augustus 2015 15:25
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: LF: Protecting a MOSFET driver chip from MOSFET failu= re?

Forgot to mention, although I hope it is more than self-ev= ident to readers here, the diode is orientated so it points 'upwards'; &nbs= p;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 <andy.g4jnt@gm= ail.com> wrote:
Yes there is.  Or , are: several.

Don't drive the MOSFET directly from the IC.  Instead use a capac= itor and DC restorer circuit.  That guards against both  the driv= er 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 dio= de 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 fo= rced 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 <chris@chriswi= lson.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
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 w= as
not able to get an antenna sorted in time.




--


Best regards,
 Chris                  &= nbsp;         mailto:chris@chriswilson.tv




--_000_7E7DFBB4D102A04DB5ADC88D66628A4A443E0BC1ICTSSMBX1lunaku_--