Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by klubnl.pl (8.14.4/8.14.4/Debian-8+deb8u2) with ESMTP id x1OEku67017020 for ; Sun, 24 Feb 2019 15:47:03 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1gxuz0-0006zL-JG for rs_out_1@blacksheep.org; Sun, 24 Feb 2019 14:42:22 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1gxuz0-0006zC-2o for rsgb_lf_group@blacksheep.org; Sun, 24 Feb 2019 14:42:22 +0000 Received: from mail-vk1-xa2d.google.com ([2607:f8b0:4864:20::a2d]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.91) (envelope-from ) id 1gxuyx-0003Pk-Fu for rsgb_lf_group@blacksheep.org; Sun, 24 Feb 2019 14:42:21 +0000 Received: by mail-vk1-xa2d.google.com with SMTP id 89so1545302vkq.7 for ; Sun, 24 Feb 2019 06:42:19 -0800 (PST) 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=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to; bh=T9L/as5nZ65Xzik/RrHk2uPI8dq8cC9Qt6Ya85XRAP0=; b=NVZFZ1f9twE9/5MX6IBJ2auuPJHLUMSWZv5RtX2MLXELMR4I4Xf5jAdznbGewTdtzv baqeMDFIptDd+dpZY0tEp+WprAFJHzxtLKIj1S2S9Cx8NwRyeX6YjDbOPRBlO8NzY3ZF vH0qaMjBmWViKejdLlF4oHctcOsF3E6CkMyZBKKkBcPT5OGjfYKUmkKsU+pmQ7erBkJx o+6ZrtbPzEPvbLg5nY6bJdZCrAnpS6GEn9EjKCFWJnsKqmAzd7qgUU8vIrWEgRKdniv8 cWEml6JtC9Qbb4MuaJ5HZqAdSIOLbURvsx9CIvrhlwU1gItsub4r98dgCDNtuSceEEod pkEA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to; bh=T9L/as5nZ65Xzik/RrHk2uPI8dq8cC9Qt6Ya85XRAP0=; b=RgpIJMFfM0mFjVcjY35omyuFe8V6CzDlo2cSeGfyI0UcTTGIGN3ep3LfG3kSrLVMPu SVKPplOBfbgIwhr8aRnRdvAQfs8y3WmJtgyEIqSYIGKUPDQhCFvH5JihlMAkgxIoxUfi fa0hWNJSSNECjpXjQavMwYEtTgH3Toh7qn8hTmfQ6YOEc/ChEXWgcaxGVwzo8bdrEeJO ngLnfRVGAvnnsl7BSesnHbMj45w23YO7S33SWlYM0myJU5nyxwks8Lb3dfffZATnRVdJ Cae1k4KPD763bu1Zu5ethQZch+SCrIVWnaEbsfYrnuxIJ+h5qC6vAh4ShB25fD6BJsQp pGEA== X-Gm-Message-State: AHQUAuYbHCJetIGBvLeaxOxQYLjey0WWZ06E73ZOfRFlXi5p/+YalJvi fN0AzFzD9h1EAIhaRAOkt9tgEX1/clTI/h39hblAPQ== X-Google-Smtp-Source: AHgI3IauS+uaD/jz1+gK6eYpGSyIGkZJjJLOgfqZgSGTfnEGg4iH3rQ3nXwS8FnwdULX2KB8mlR1XPM8VbS/mWKwxZU= X-Received: by 2002:a1f:a689:: with SMTP id p131mr7194058vke.67.1551019337600; Sun, 24 Feb 2019 06:42:17 -0800 (PST) MIME-Version: 1.0 References: <043bec62-8144-5ff3-98a6-9f04699f6a4c@no3m.net> <1551011916482.41235@kuleuven.be> <1551014480338.17397@kuleuven.be> <27248150-3565-aeb8-9b66-53a9089fd4ab@n1bug.com> <1551018171015.45843@kuleuven.be> In-Reply-To: <1551018171015.45843@kuleuven.be> From: Andy Talbot Date: Sun, 24 Feb 2019 14:41:57 +0000 Message-ID: To: "rsgb_lf_group@blacksheep.org" X-Spam-Score: 0.0 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has NOT identified this incoming email as spam. The original message has been attached to this so you can view it or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: For on-off keying of a switch mode PA you really should be using supply line control. Switching the drive then trying to reduce rise /fall times for keyclick elimination by controlling drive amplitude [...] Content analysis details: (0.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [2607:f8b0:4864:20:0:0:0:a2d listed in] [list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (andy.g4jnt[at]gmail.com) 0.0 HTML_MESSAGE BODY: HTML included in message X-Scan-Signature: 2b323379b582abbe78ea971e119c2a1c Subject: Re: LF: Re: Class D current spikes Content-Type: multipart/alternative; boundary="000000000000a854990582a4d4a4" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.5 required=5.0 tests=HTML_20_30,HTML_MESSAGE, TO_ADDRESS_EQ_REAL autolearn=no version=2.63 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 --000000000000a854990582a4d4a4 Content-Type: text/plain; charset="UTF-8" For on-off keying of a switch mode PA you really should be using supply line control. Switching the drive then trying to reduce rise /fall times for keyclick elimination by controlling drive amplitude(something that seems to be done in some designs) is really asking for trouble. Even hard-switching drive gives its problems , as we see here repeatedly Instead, why not a simple emitter follower in the positive supply, then you can apply waveform shaping to the base drive at low current, where you've got full control. Even a 20A supply could be controlled this way with a suitably rated transistor. Quite likely have to be a Darlington. There will be a slight fixed drop across it, say 1V at saturation / full power, so a few watts of dissipation, but it's only operating non saturated for a short period during the rise / fall times. A power FET could be used, but you'd need a drive voltage Vgs higher than the supply, albeit only a few mA capability; nothing a small switcher module couldn't manage. Andy www.g4jnt.com On Sun, 24 Feb 2019 at 14:26, Rik Strobbe wrote: > Hello Paul, Eric, Andy, > > AC coupling with a large C will not solve the problem. > At "key up" one of the driver outputs will remain high thus the gate of > theFET connected to that output will remain high (and the FET conducting) > during a time depending on RC constant of the driver / gate network. For > 0.22uF and 4.7kOhm the RC constant is 1 millisecond. So for a driver > running on 12V iit will take about that time for the gate voltage to drop > below the treshold. During that 1ms the FET is more or less shortcircuiting > the powersupply. One of them will die sooner ot later ;-) > > 73, Rik ON7YD - OR7T > ________________________________________ > Van: owner-rsgb_lf_group@blacksheep.org < > owner-rsgb_lf_group@blacksheep.org> namens N1BUG > Verzonden: zondag 24 februari 2019 15:03 > Aan: rsgb_lf_group@blacksheep.org > Onderwerp: Re: LF: Re: Class D current spikes > > I will be watching this discussion closely. Mine is a W1VD kilowatt > deck: > > http://w1vd.com/137-500-KWRev3.0.pdf > > It has blown FETs several times. The problem always occurs at the > end of the RF envelope. To further confuse this issue, I have lost > only one FET while running with my U3S exciter in hundreds of hours > of operation. I have lost many FETs when driving it with HF > transceiver and down converter. I have also lost FETs driving it > with a phasing exciter. It seems using it with either of the latter > exciters almost guarantees one or more dead FETs within a few > minutes. I was running at about 300 watts output during all of these > failures. > > 73, > Paul > > > On 2/24/19 8:42 AM, Eric NO3M wrote: > > The driver and FET gates in mine are AC coupled (0.22u, SB560 > > schottky shunt, 10 ohm series, 4.7k shunt) and the problem still > > exists. Apparently same thing Paul N1BUG was having problems with. > > The spike on the end of the RF envelope is what seems most ominous > > and results in my 48v switcher going into fault mode. > > > --000000000000a854990582a4d4a4 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
For on-off keying of a switch mode PA you really= should be using supply line control.=C2=A0 Switching the drive then trying= to reduce rise /fall times for keyclick elimination by controlling drive a= mplitude(something that seems to be done in some designs) is really asking = for trouble.=C2=A0 Even hard-switching drive gives its problems , as we see= here repeatedly

Instead, why not a simp= le emitter follower in the positive supply, then you can apply waveform sha= ping=C2=A0 to the base drive at low current, where you've got full cont= rol.=C2=A0 =C2=A0Even a 20A supply could be controlled this way with a suit= ably rated transistor.=C2=A0 Quite likely have to be a Darlington.=C2=A0 = =C2=A0There will be a slight fixed drop across it, say 1V at saturation / f= ull power, so a few watts of dissipation, but it's only operating non s= aturated for a short period during the rise / fall times.
=
A power FET could be used, but you'd need a drive v= oltage Vgs higher than the supply, albeit only a few mA capability; nothing= a small switcher module couldn't manage.
=C2=A0
<= /div>


On Sun, 24 Feb 2019 at 14:26, Rik Strobbe <rik.strobbe@kuleuven.be> wr= ote:
Hello Paul,= Eric, Andy,

AC coupling with a large C will not solve the problem.
At "key up" one of the driver outputs will remain high thus the g= ate of theFET connected to that output will remain high (and the FET conduc= ting) during a time depending on=C2=A0 RC constant of the driver / gate net= work. For 0.22uF and 4.7kOhm the RC constant is 1 millisecond. So for a dri= ver running on 12V iit will take about that time for the gate voltage to dr= op below the treshold. During that 1ms the FET is more or less shortcircuit= ing the powersupply. One of them will die sooner ot later ;-)

73, Rik=C2=A0 ON7YD - OR7T
________________________________________
Van: owner-rsgb_lf_group@blacksheep.org <owner-rsgb_lf_group@blacksheep.or= g> namens N1BUG <paul@n1bug.com>
Verzonden: zondag 24 februari 2019 15:03
Aan: rsgb= _lf_group@blacksheep.org
Onderwerp: Re: LF: Re: Class D current spikes

I will be watching this discussion closely. Mine is a W1VD kilowatt
deck:

http://w1vd.com/137-500-KWRev3.0.pdf

It has blown FETs several times. The problem always occurs at the
end of the RF envelope. To further confuse this issue, I have lost
only one FET while running with my U3S exciter in hundreds of hours
of operation. I have lost many FETs when driving it with HF
transceiver and down converter. I have also lost FETs driving it
with a phasing exciter. It seems using it with either of the latter
exciters almost guarantees one or more dead FETs within a few
minutes. I was running at about 300 watts output during all of these
failures.

73,
Paul


On 2/24/19 8:42 AM, Eric NO3M wrote:
> The driver and FET gates in mine are AC coupled (0.22u, SB560
> schottky shunt, 10 ohm series, 4.7k shunt) and the problem still
> exists.=C2=A0 Apparently same thing Paul N1BUG was having problems wit= h.
> The spike on the end of the RF envelope is what seems most ominous
> and results in my 48v switcher going into fault mode.


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