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=-1.6 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, HTML_40_50,HTML_BACKHAIR_8,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 t7AFJv4a025768 for ; Mon, 10 Aug 2015 17:19:57 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ZOopB-00053t-2d for rs_out_1@blacksheep.org; Mon, 10 Aug 2015 16:17:17 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ZOopA-00053k-LG for rsgb_lf_group@blacksheep.org; Mon, 10 Aug 2015 16:17:16 +0100 Received: from mail-wi0-f173.google.com ([209.85.212.173]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.86) (envelope-from ) id 1ZOoo9-0002Yy-Fj for rsgb_lf_group@blacksheep.org; Mon, 10 Aug 2015 16:17:15 +0100 Received: by wicne3 with SMTP id ne3so26281562wic.0 for ; Mon, 10 Aug 2015 08:15:57 -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=U8ADuN6h5DVuLodDaeRWuStj4gsFZEy7T2MPa/d3nnQ=; b=L7tA1y32ozZ2cearrjzXX1tPaLsH+vJ7Jn1a7WW3wjqrqLbKwP/fbcg2bidiPmfVwb 4ousf1gogjtnOv1cr0ZAFMC9DnvEI23IiImhgqBoTFhxVq8d+QW7PiOydhHfsuF3bL/r MNXnCbwVIbHNzdvSktGeHNZsRNI4Xq1s+9emPZ/LlaK4Z0KjJBsoNP5MAs6Ne7vowGo+ Sh55Lq4CcgSFIU74NJSFZZLBD3EWr/x2HDYJtsJXGWxuSViMYolomLLKCnl5xzNL9y0J hu7UkFOCeSdwE7NzMKa6Y86e62wnCquzuiSF592KTH8ogd41D79iI34V+hLSgPHYhBKC 18SQ== MIME-Version: 1.0 X-Received: by 10.180.105.165 with SMTP id gn5mr24488373wib.20.1439219757506; Mon, 10 Aug 2015 08:15:57 -0700 (PDT) Received: by 10.28.98.6 with HTTP; Mon, 10 Aug 2015 08:15:57 -0700 (PDT) In-Reply-To: <7E7DFBB4D102A04DB5ADC88D66628A4A443E0BC1@ICTS-S-MBX1.luna.kuleuven.be> References: <1892164761.20150810130954@chriswilson.tv> <7E7DFBB4D102A04DB5ADC88D66628A4A443E0BC1@ICTS-S-MBX1.luna.kuleuven.be> Date: Mon, 10 Aug 2015 16:15:57 +0100 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org X-Scan-Signature: ce3df9f2acd7587159138e0455ceb9aa Subject: Re: LF: Protecting a MOSFET driver chip from MOSFET failure? Content-Type: multipart/alternative; boundary=f46d041826986666dc051cf67602 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: 3846 --f46d041826986666dc051cf67602 Content-Type: text/plain; charset=UTF-8 No, capacitive coupling *with diode restoration* ends up with near-enough the same voltage applied to the gate as you had in thr first place. A 0/12v output from the driver chips ends up at -0.7 /+ 11.3 V (assuming 0.7V diode drop) As for the question of the dual drive with resistors. The resistors may as well say in, just to smooth off edges and reduce dissipation in the driver. i doubt you'll notice any difference. Andy G4JNT On 10 August 2015 at 15:35, Rik Strobbe wrote: > 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 switching of the MOSFET. > > If you use a transformer (as suggested by Stefan) one can fiddle with > the transformer 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 >> 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 >>> >>> >>> >> > --f46d041826986666dc051cf67602 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
No, capacitive coupling with diode restoration ends= up with near-enough =C2=A0the same voltage applied to the gate as you had = in thr first place.

A 0/12v output from the driver chips ends = up at -0.7 /+ 11.3 V (assuming 0.7V diode drop)

As for the question of the dual drive with resistors. =C2=A0 = =C2=A0The resistors may as well say in, just to smooth off edges and reduce= dissipation in the driver. =C2=A0 =C2=A0 i doubt you'll notice any dif= ference.

Andy =C2=A0G4JNT


On 10 August 2015 at 15:35, Rik St= robbe <Rik.Strobbe@fys.kuleuven.be> wrote:

Maybe=C2=A0also=C2=A0worth to mention:=C2=A0= =C2=A0Capacitive=C2=A0coupling of the=C2=A0driver to t= he=C2=A0gate=C2=A0will=C2=A0reduce the=C2=A0peak voltage at the=C2=A0gate=C2=A0by=C2=A0h= alf (assuming 50%=C2=A0duty cycle).

The IC=C2=A0driver voltage=C2=A0should=C2=A0be at=C2=A0least=C2=A012V in order to=C2=A0ensu= re proper=C2=A0switching of the MOSFET.

If=C2=A0you=C2=A0use a=C2=A0transformer (as= =C2=A0suggested=C2=A0by Stefan)=C2=A0one=C2=A0can=C2=A0fiddle=C2=A0with the=C2=A0transformer ratio to=C2=A0get the proper voltage at= the gate.

=C2=A0

73,=C2=A0Rik=C2=A0=C2=A0ON7YD - OR7T<= a>

=C2=A0

Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blac= ksheep.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= 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@gm= ail.com> wrote:
Yes there is.=C2=A0 Or , are: several.

Don't drive the MOSFET directly from the IC.=C2=A0 Instead use a c= apacitor and DC restorer circuit.=C2=A0 That guards against both =C2=A0the = driver staying high permanently if drive is removed, and also against IC da= mage if the FET fails

Capacitor (typically 100nF for 137/475kHz) from IC output to gate
Diode like IN914 , 1N4148 etc from gate to ground.=C2=A0 Shunt the dio= de with a resistor of a few kohms to stop it floating

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

Or use transformer coupling, as in my QRO 137kHz transmitter. =C2=A0http://www.g4jnt= .com/137tx.pdf

Andy =C2=A0G4JNT


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<= 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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