Return-Path: Received: from mtain-me01.r1000.mx.aol.com (mtain-me01.r1000.mx.aol.com [172.29.96.137]) by air-me03.mail.aol.com (v129.4) with ESMTP id MAILINME033-8baa4d2f3a36f7; Thu, 13 Jan 2011 12:45:26 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-me01.r1000.mx.aol.com (Internet Inbound) with ESMTP id 5DA0F38000081; Thu, 13 Jan 2011 12:45:25 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PdRE6-0007bM-4z for rs_out_1@blacksheep.org; Thu, 13 Jan 2011 17:44:46 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PdRE5-0007bB-Ol for rsgb_lf_group@blacksheep.org; Thu, 13 Jan 2011 17:44:45 +0000 Received: from out1.ip01ir2.opaltelecom.net ([62.24.128.237]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PdRE3-0000Js-4E for rsgb_lf_group@blacksheep.org; Thu, 13 Jan 2011 17:44:45 +0000 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Ai0GAOrILk1cHYxR/2dsb2JhbACISY1rjhRzvTGFTASOTA X-IronPort-AV: E=Sophos;i="4.60,318,1291593600"; d="scan'208";a="339694324" Received: from unknown (HELO xphd97xgq27nyf) ([92.29.140.81]) by out1.ip01ir2.opaltelecom.net with SMTP; 13 Jan 2011 17:44:36 +0000 Message-ID: <004001cbb349$8b4ec190$0401a8c0@xphd97xgq27nyf> From: "mal hamilton" To: References: <003801cbb33e$8b59e620$0401a8c0@xphd97xgq27nyf> Date: Thu, 13 Jan 2011 17:44:35 -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,none Subject: LF: Re: Re: FET RDS Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit 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=none 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: 3039ac1d60894d2f3a356eb9 X-AOL-IP: 195.171.43.25 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 > > >