Return-Path: X-Spam-DCC: paranoid 1481; 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,SPF_PASS 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 uAPEN33P029409 for ; Fri, 25 Nov 2016 15:23:03 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1cAHLS-0001br-RL for rs_out_1@blacksheep.org; Fri, 25 Nov 2016 14:19:18 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1cAHLS-0001bi-Fp for rsgb_lf_group@blacksheep.org; Fri, 25 Nov 2016 14:19:18 +0000 Received: from mail-wj0-x22c.google.com ([2a00:1450:400c:c01::22c]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.87) (envelope-from ) id 1cAHLM-00044F-Mx for rsgb_lf_group@blacksheep.org; Fri, 25 Nov 2016 14:19:17 +0000 Received: by mail-wj0-x22c.google.com with SMTP id mp19so60310288wjc.1 for ; Fri, 25 Nov 2016 06:19:12 -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=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to; bh=z1o3MDn4k/gIgDK7XrI53sBZ2VGtD3nFbVf6+2KucOM=; b=RvrG1pS7SilbJMmIyaNftvgwuxRGYDTFKHve2DmlZwhG7ziUdXycvMJJ+I9D+wesgD cWso9E39e7pmCKdbOWf2eTq9Mb/o66WWRKO3/QFcwOSB700su4l28Lk1zKFe71L5Th+R EL0isOHDo2i8B6c4K/nCdff6TezKeRywmEtF9NVkhndt1zHJ1X+sttscwdga0k5Mhqxf LWJAsUAE5ZoAed/XfiwnKquw1o5zPPeLkQYD88VUTMvSYOutbXKPNmGeM5wmh7tm7oBO g3GBVmn3grLjOijNL9csl08sXGC+sprZ4RNXe1FA+T5I43UWabrGiK4qH8zjF5n/u7PJ FYAA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to; bh=z1o3MDn4k/gIgDK7XrI53sBZ2VGtD3nFbVf6+2KucOM=; b=fZjk00WZTT8sPXT37vpa6SWunwl/BYJpYdsvgjJEvrVGz02ZJZYwU6UtR8DOBqQlW7 kMzUdiZC3BYny2Z68+zPlkkfQW9dpGEYq1lGmgG5kF+NpNYu9uveHSesWUTiDLxfKzZk zDwseH73VDbnZ41xwnQQrkOLjaLo/1Ydx1hBB000O5q8eibyng3NbWxdVeAinbljnSXi +DbWpp78Qe/EMJY3kyTctm+zQo3LSQqBVmrYQY6Ivwc75knR+eGKiiM7RoGIYdcBFR8d X73woRF4LzH/458siLWJlobYWuAYbjYRK8uaC0srGYVcb9jaHkTKJHakewuZqUcP1Wmv WmSQ== X-Gm-Message-State: AKaTC00Mw6ePnR1+ogaiddd3pRlcuACaGX4/lsI18/NpoprHgRYxIbdTMPrZ8GTjw5u+HJ38gMlciV8CxqOD5Q== X-Received: by 10.194.95.194 with SMTP id dm2mr7468829wjb.207.1480083551330; Fri, 25 Nov 2016 06:19:11 -0800 (PST) MIME-Version: 1.0 Received: by 10.28.91.1 with HTTP; Fri, 25 Nov 2016 06:19:10 -0800 (PST) In-Reply-To: References: <635074543.20161125135600@chriswilson.tv> From: Andy Talbot Date: Fri, 25 Nov 2016 14:19:10 +0000 Message-ID: To: rsgb_lf_group@blacksheep.org X-Scan-Signature: 18c242620d7d7b91a1caf5740aa3e326 Subject: Re: LF: H Bridge power MOSFET based amps question Content-Type: multipart/alternative; boundary=047d7b624eec50a825054220ce33 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 10.1.3.11 Content-Length: 6501 Status: O X-Status: X-Keywords: X-UID: 9544 --047d7b624eec50a825054220ce33 Content-Type: text/plain; charset=UTF-8 Forget my comments about gate resistors, you said for a non linear (switching) design. I was talking about linear amps As the last post said, small values to damp oscillations if any are needed at all - assuming a proper square wave drive, they shouldn't be. 'JNT On 25 November 2016 at 14:16, Andy Talbot wrote: > continuing... > > The gate resistor just has to swamp teh Xc of the gate capacitance in a > linear amp, to make it look clean and resistive at the input. So, for > example, assume 2000pF Cgs at 475kHz. Xc = 167 ohms. SO a shunt R of > say 30 to 50 ohms will dominate. > If you were really daring you might think it possible to resonate out the > Gate C and then get really high gain. ( Don't do this with an expensive > FET). But worth trying the experiment to see - power oscillators take on > a completely new meaning if you try it. > > drain / source... emitter / collector. They're just legacy names. You > just know what they are without thinking of the actual meaning. Although, > I suppose, if you think of electron flow........... > > 'JNT > > > > > On 25 November 2016 at 13:56, Chris Wilson wrote: > >> 25 November 2016 >> >> >> I have built a 1kW Class D amp for none linear digital transmissions >> around 136kHz. >> >> My Dave Pick designed amp uses four MOSFETS, two in parallel each side >> driven by a dedicated driver chip. I see the odd LF amp design using >> what's described as a H Bridge MOSFET array. The one I most recall >> most, by Andy Talbot used rectified 240 volt single phase mains to run >> it. My question is why use an H Bridge rather than paralleling more >> MOSFETS in what to me is a more conventional format? Does it overcome >> voltage or current limitations? Is it due to adding more capacitance >> with paralleled devices? Or does it allow a linear amp to be built? >> >> I realize a meaningful reply might be quite lengthy, so I assure you I >> have Googled it, but most stuff related to in the articles is >> industrial motor control. >> >> Secondly, in a Class D none linear amp, how is the gate resistor value >> chosen, and is there ever a case for not using one at all? >> >> Thirdly, am I alone in thinking the terms Drain and Source seem back >> to front and the names would intuitively be reversed so a Drain was >> called a Source and vice versa? :) >> >> Thanks. 2E0ILY >> >> >> >> -- >> >> >> Best regards, >> Chris 2E0ILY mailto:chris@chriswilson.tv >> >> >> >> > --047d7b624eec50a825054220ce33 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Forget my comments about gate resistors, you said for a no= n linear (switching) design.=C2=A0 I was talking about linear amps
As t= he last post said, small values to damp oscillations if any are needed at a= ll - assuming a proper square wave drive, they shouldn't be.
=
'JNT

On 25 November 2016 at 14:16, Andy Talbot <andy.g4jnt= @gmail.com> wrote:
continuing...

The gate resistor just has to swa= mp teh Xc of the gate capacitance in a linear amp, to make it look clean an= d resistive at the input.=C2=A0 So, for example, assume 2000pF =C2=A0Cgs at= 475kHz. =C2=A0 Xc =3D 167 ohms. =C2=A0 SO a shunt R of say 30 to 50 ohms w= ill dominate. =C2=A0 =C2=A0
If you were really daring you might t= hink it possible to resonate out the Gate C and then get really high gain. = =C2=A0 ( Don't do this with an expensive FET). =C2=A0 But worth trying = the experiment to see - power oscillators take on a completely new meaning = if you try it.

drain / source... =C2=A0 emitter / = collector.=C2=A0 They're just legacy names.=C2=A0 You just know what th= ey are without thinking of the actual meaning. =C2=A0 Although, I suppose, = if you think of electron flow...........

'JNT<= /div>




On 25 November 2016 at 13:56, Chris Wilson= <chris@chriswilson.tv> wrote:
25 November 2016


I have built a 1kW Class D amp for none linear digital transmissions
around 136kHz.

My Dave Pick designed amp uses four MOSFETS, two in parallel each side
driven by a dedicated driver chip. I see the odd LF amp design using
what's described as a H Bridge MOSFET array. The one I most recall
most, by Andy Talbot used rectified 240 volt single phase mains to run
it. My question is why use an H Bridge rather than paralleling more
MOSFETS in what to me is a more conventional format? Does it overcome
voltage or current limitations? Is it due to adding more capacitance
with paralleled devices? Or does it allow a linear amp to be built?

I realize a meaningful reply might be quite lengthy, so I assure you I
have Googled it, but most stuff related to in the articles is
industrial motor control.

Secondly, in a Class D none linear amp, how is the gate resistor value
chosen, and is there ever a case for not using one at all?

Thirdly, am I alone in thinking the terms Drain and Source seem back
to front and the names would intuitively be reversed so a Drain was
called a Source and vice versa? :)

Thanks. 2E0ILY



--


Best regards,
=C2=A0Chris=C2=A0 2E0ILY=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=A0mailto:chris@chriswilson.tv





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