Return-Path: Received: from mtain-md03.r1000.mx.aol.com (mtain-md03.r1000.mx.aol.com [172.29.96.87]) by air-dc08.mail.aol.com (v129.4) with ESMTP id MAILINDC084-86a64d2f3ed2205; Thu, 13 Jan 2011 13:05:06 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-md03.r1000.mx.aol.com (Internet Inbound) with ESMTP id 77771380000C6; Thu, 13 Jan 2011 13:05:04 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PdRWx-00087p-Sv for rs_out_1@blacksheep.org; Thu, 13 Jan 2011 18:04:15 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PdRWx-00087g-Cj for rsgb_lf_group@blacksheep.org; Thu, 13 Jan 2011 18:04:15 +0000 Received: from out1.ip09ir2.opaltelecom.net ([62.24.128.245]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PdRWv-0000cI-1h for rsgb_lf_group@blacksheep.org; Thu, 13 Jan 2011 18:04:15 +0000 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AjQFAF/NLk1cHYxR/2dsb2JhbACSHgOSKnO9IoVMBIFejG6CWw X-IronPort-AV: E=Sophos;i="4.60,318,1291593600"; d="scan'208,217";a="464683233" Received: from unknown (HELO xphd97xgq27nyf) ([92.29.140.81]) by out1.ip09ir2.opaltelecom.net with SMTP; 13 Jan 2011 18:04:05 +0000 Message-ID: <005801cbb34c$44624b50$0401a8c0@xphd97xgq27nyf> From: "mal hamilton" To: References: <003801cbb33e$8b59e620$0401a8c0@xphd97xgq27nyf><004001cbb349$8b4ec190$0401a8c0@xphd97xgq27nyf> Date: Thu, 13 Jan 2011 18:04:05 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 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="----=_NextPart_000_0055_01CBB34C.441F75F0" 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 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-sid: 3039ac1d60574d2f3ed02337 X-AOL-IP: 195.171.43.25 ------=_NextPart_000_0055_01CBB34C.441F75F0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Anything above 70% is respectable especially if it cost nil for compon= ents and occassional use. de mal/g3kev ----- Original Message -----=20 From: Andy Talbot=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Thursday, January 13, 2011 5:55 PM Subject: Re: LF: Re: Re: FET RDS If I can get 80% for 400V on 500kHz using a pair of cheap and cheerf= ul FETs cobbled together, 90% plus should be easy-enough by spending= a bit of time and effort on their selection. =20 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.=20 So its hardly rocket science. Andy www.g4jnt.com =20 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 da= y 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 av= ailable > 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 increa= se Vdc to > about 100V, or reduce it to about 40V and use lower Rdson 200V= mosfets. > > Cheers, Jim Moritz > 73 de M0BMU > > > ------=_NextPart_000_0055_01CBB34C.441F75F0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Anything above 70% is respectable esp= ecially if it=20 cost nil for components and occassional use.
de mal/g3kev
 
----- Original Message -----
From:=20 Andy=20 Talbot
Sent: Thursday, January 13,= 2011 5:55=20 PM
Subject: Re: LF: Re: Re: FET= RDS

If I can get 80% for 400V on 500kHz using a pair of cheap= and=20 cheerful FETs cobbled together, 90% plus should be easy-enough by sp= ending a=20 bit of time and effort on their selection.   
A while back I managed greater than 85% on a 20W class E= topband PA,=20 and that is an overall efficiency figure,  including power take= n by=20 driver stages and dropped in linear regulators. 
So its hardly rocket science.
 
Andy
 


 
On 13 January 2011 17:44, mal hamilton <g3kev= mal@talktalk.net>=20 wrote:
Jim
What=20 you say is correct but it is virtually impossible to achieve the= 90%
plus=20 efficiency claimed by some. The FET required in practice is notavailable=20 and these high efficiencies are only theoritical.
I have found= this in=20 practice ie 80% if you are lucky on a good day
mal/g3kev

-----=20 Original Message -----
From: "James Moritz" <james.moritz@btopenworld.com<= /A>>
To:=20 <rsgb_lf_= group@blacksheep.org>
Sent:=20 Thursday, January 13, 2011 5:31 PM
Subject: LF: Re: FET=20 RDS


> Dear Mal, Andy, LF Group,
>
> Ther= e is a=20 trade-off in construction of MOSFETs - basically, for a given
&= gt; area=20 of silicon,  higher BVdss requires a thicker active region of= =20 the
> MOSFET with higher on resistance. You can reduce Rdson= by using=20 a greater
> chip area, but that means higher capacitances,= increased=20 cost, etc. So you
> can't have your cake and eat it.
>=
>=20 In Andy's breadboard circuit, there is a mismatch between the=20 available
> MOSFET type and the available PSU voltage - the= 500V BVdss=20 is a bit too
high
> for a 60V DC supply - the peak voltag= e in an=20 ideal class E is 3.56 x Vdc,
> perhaps you would allow 5 x= Vdc for=20 safety. 300V BVdss mosfets seem a bit
> thin on the ground,= so more=20 efficient schemes might be to increase Vdc to
> about 100V,= or reduce=20 it to about 40V and use lower Rdson 200V mosfets.
>
>= Cheers,=20 Jim Moritz
> 73 de=20 M0BMU
>
>
>



------=_NextPart_000_0055_01CBB34C.441F75F0--