Return-Path: Received: from mtain-mg08.r1000.mx.aol.com (mtain-mg08.r1000.mx.aol.com [172.29.96.208]) by air-md03.mail.aol.com (v129.4) with ESMTP id MAILINMD033-8b7e4d2f3cd632f; Thu, 13 Jan 2011 12:56:38 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-mg08.r1000.mx.aol.com (Internet Inbound) with ESMTP id 0683638000106; Thu, 13 Jan 2011 12:56:36 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PdROj-000801-Iu for rs_out_1@blacksheep.org; Thu, 13 Jan 2011 17:55:45 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PdROj-0007zs-2L for rsgb_lf_group@blacksheep.org; Thu, 13 Jan 2011 17:55:45 +0000 Received: from mail-iy0-f171.google.com ([209.85.210.171]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PdROg-0000X1-NL for rsgb_lf_group@blacksheep.org; Thu, 13 Jan 2011 17:55:45 +0000 Received: by iyj21 with SMTP id 21so1849687iyj.16 for ; Thu, 13 Jan 2011 09:55:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:in-reply-to:references:date :message-id:subject:from:to:content-type; bh=IpHxympfCOkNQGJZ7yeduLFb22YYGzkmcjzsrNfFDmc=; b=mm520fakARLFY1hoH54fNj3eX/EKkvW05/SMbMO2ZTZHpajQfwR2/cYF6PLXKa7AFs ET4BuMiGQDFfb0zB54DOYNrObAButfVuWsRX5s7grcG54dHPbiqfClCfvgl9Fp5N4aJT 8bmJ69HHuPXc0SAdYFeJRpGoGlyCiYX1IGcBw= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=SS6j9qnbMH+MSCsjKuVHx2CHTElZxML2Jsr+IHIxV9CVVzFrjKvUTZkNHUdOLk/p9q 3DMj/PL1yoFwBGmp5OoLkxIVpMJEGzsCUYjJqIozJ5xKG76ay20plMlWABiAJe3lpeI9 qUVBCjk2sq+U5cIZrv/S/0bWuBd2tmOTagAx8= MIME-Version: 1.0 Received: by 10.231.207.73 with SMTP id fx9mr2638401ibb.137.1294941336532; Thu, 13 Jan 2011 09:55:36 -0800 (PST) Received: by 10.231.200.211 with HTTP; Thu, 13 Jan 2011 09:55:36 -0800 (PST) In-Reply-To: <004001cbb349$8b4ec190$0401a8c0@xphd97xgq27nyf> References: <003801cbb33e$8b59e620$0401a8c0@xphd97xgq27nyf> <004001cbb349$8b4ec190$0401a8c0@xphd97xgq27nyf> Date: Thu, 13 Jan 2011 17:55:36 +0000 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: Re: Re: FET RDS Content-Type: multipart/alternative; boundary=90e6ba53a55e5e78610499be0616 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=HTML_MESSAGE 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 x-aol-global-disposition: G X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d221.2 ; domain : gmail.com DKIM : pass x-aol-sid: 3039ac1d60d04d2f3cd426a9 X-AOL-IP: 195.171.43.25 X-Mailer: Unknown (No Version) --90e6ba53a55e5e78610499be0616 Content-Type: text/plain; charset=ISO-8859-1 If I can get 80% for 400V on 500kHz using a pair of cheap and cheerful FETs cobbled together, 90% plus should be easy-enough by spending a bit of time and effort on their selection. A while back I managed greater than 85% on a 20W class E topband PA, and that is an overall efficiency figure, including power taken by driver stages and dropped in linear regulators. So its hardly rocket science. Andy www.g4jnt.com On 13 January 2011 17:44, mal hamilton wrote: > Jim > What you say is correct but it is virtually impossible to achieve the 90% > plus efficiency claimed by some. The FET required in practice is not > available and these high efficiencies are only theoritical. > I have found this in practice ie 80% if you are lucky on a good day > mal/g3kev > > > ----- Original Message ----- > From: "James Moritz" > To: > Sent: Thursday, January 13, 2011 5:31 PM > Subject: LF: Re: FET RDS > > > > Dear Mal, Andy, LF Group, > > > > There is a trade-off in construction of MOSFETs - basically, for a given > > area of silicon, higher BVdss requires a thicker active region of the > > MOSFET with higher on resistance. You can reduce Rdson by using a greater > > chip area, but that means higher capacitances, increased cost, etc. So > you > > can't have your cake and eat it. > > > > In Andy's breadboard circuit, there is a mismatch between the available > > MOSFET type and the available PSU voltage - the 500V BVdss is a bit too > high > > for a 60V DC supply - the peak voltage in an ideal class E is 3.56 x Vdc, > > perhaps you would allow 5 x Vdc for safety. 300V BVdss mosfets seem a bit > > thin on the ground, so more efficient schemes might be to increase Vdc to > > about 100V, or reduce it to about 40V and use lower Rdson 200V mosfets. > > > > Cheers, Jim Moritz > > 73 de M0BMU > > > > > > > > > --90e6ba53a55e5e78610499be0616 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
If I can get 80% for 400V on 500kHz=A0using a pair of cheap and cheer= ful FETs cobbled together, 90% plus should be easy-enough by spending a bi= t of time and effort on their selection.=A0=A0=A0
A while back I=A0managed greater than 85% on a 20W class E topband PA= , and that is an overall efficiency figure, =A0including power taken by dr= iver stages and dropped in linear regulators.=A0
So its hardly rocket science.
=A0
Andy
=A0


=A0
On 13 January 2011 17:44, mal hamilton <g3kevmal@talktalk.n= et> wrote:
Jim
What you say is correct= but it is virtually impossible to achieve the 90%
plus efficiency clai= med by some. The FET required in practice is not
available and these high efficiencies are only theoritical.
I have foun= d this in practice ie 80% if you are lucky on a good day
mal/g3kev
<= br>
----- Original Message -----
From: "James Moritz" <= james.moritz@btopenworld.c= om>
To: <rsgb_lf_group@blac= ksheep.org>
Sent: Thursday, January 13, 2011 5:31 PM
Subject:= LF: Re: FET RDS


> Dear Mal, Andy, LF Group,
>
>= There is a trade-off in construction of MOSFETs - basically, for a given<= br> > area of silicon, =A0higher BVdss requires a thicker active region of= the
> MOSFET with higher on resistance. You can reduce Rdson by usi= ng a greater
> chip area, but that means higher capacitances, increa= sed cost, etc. So you
> can't have your cake and eat it.
>
> In Andy's br= eadboard circuit, there is a mismatch between the available
> MOSFET= type and the available PSU voltage - the 500V BVdss is a bit too
high<= br> > for a 60V DC supply - the peak voltage in an ideal class E is 3.56 x= Vdc,
> perhaps you would allow 5 x Vdc for safety. 300V BVdss mosfe= ts seem a bit
> thin on the ground, so more efficient schemes might= be to increase Vdc to
> about 100V, or reduce it to about 40V and use lower Rdson 200V mosfet= s.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
><= br>>



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