Return-Path: <owner-rsgb_lf_group@blacksheep.org>
Received: from mtain-mi11.r1000.mx.aol.com (mtain-mi11.r1000.mail.aol.com [172.21.131.169]) by air-me01.mail.aol.com (v129.4) with ESMTP id MAILINME014-8ba34d2f3b96357; Thu, 13 Jan 2011 12:51:18 -0500
Received: from post.thorcom.com (post.thorcom.com [195.171.43.25])
	by mtain-mi11.r1000.mx.aol.com (Internet Inbound) with ESMTP id 70DAC38000087;
	Thu, 13 Jan 2011 12:51:17 -0500 (EST)
Received: from majordom by post.thorcom.com with local (Exim 4.14)
	id 1PdRJi-0007mn-Lx
	for rs_out_1@blacksheep.org; Thu, 13 Jan 2011 17:50:34 +0000
Received: from [195.171.43.32] (helo=relay1.thorcom.net)
	by post.thorcom.com with esmtp (Exim 4.14)
	id 1PdRJi-0007me-8i
	for rsgb_lf_group@blacksheep.org; Thu, 13 Jan 2011 17:50:34 +0000
Received: from out1.ip04ir2.opaltelecom.net ([62.24.128.240])
	by relay1.thorcom.net with esmtp (Exim 4.63)
	(envelope-from <g3kevmal@talktalk.net>)
	id 1PdRJf-0000Pa-Vy
	for rsgb_lf_group@blacksheep.org; Thu, 13 Jan 2011 17:50:34 +0000
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: Ai0GAKvJLk1cHYxR/2dsb2JhbACISY1ujhRzvSCCbIJgBI5Mgls
X-IronPort-AV: E=Sophos;i="4.60,318,1291593600"; 
   d="scan'208";a="320238410"
Received: from unknown (HELO xphd97xgq27nyf) ([92.29.140.81])
  by out1.ip04ir2.opaltelecom.net with SMTP; 13 Jan 2011 17:50:25 +0000
Message-ID: <004801cbb34a$5b8ab580$0401a8c0@xphd97xgq27nyf>
From: "mal hamilton" <g3kevmal@talktalk.net>
To: <rsgb_lf_group@blacksheep.org>
References: <003801cbb33e$8b59e620$0401a8c0@xphd97xgq27nyf> <4929CA3383DD45FCBC44A80A2733B139@PcMinto>
Date: Thu, 13 Jan 2011 17:50:25 -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: Re: LF: 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: 3039400cded34d2f3b950334
X-AOL-IP: 195.171.43.25


Minto
One approach is to use a few in parallel like they do in plasma tv's but
there must then be other considerations to hinder the application.
mal/g3kev

----- Original Message -----
From: "Minto Witteveen" <minto.witteveen@gmail.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, January 13, 2011 5:42 PM
Subject: Re: LF: FET RDS


> Yup that is correct. High(er) voltage fets usually have the higher RDS-on
> values... Tradeoff based on physics...
> I started my 500-600 Watts 500 KHz transverter with two IRFP360's in
> parallel.
> Later I switched to IXFH26N50 (cheaper at EUR 1 a piece and slightly
better
> than the IRFP360).
> The IXFH26N50 has a VDSS of 500 Volts, and a RDS-on of 0.23 Ohms and an Id
> of 25A.
> With two of these in parallel the efficiency is > 90%. DC supply is (max)
54
> Volts.
> Peak voltage on the drains is somewhere around max 250 Volts. So I might
> search for Fets with a somewhat lower RDSon and a lower max voltage, but
> these fets are indestructible in my setup, they survive open and
> short-circuited antennas without a problem for several minutes until heat
> becomes a problem.
>
>
> For more info wrt my setup see www.pa3bca.nl
>
> Regards,
> Minto pa3bca (500 KHz in PA idle at the moment, alas...)
>
>
>
>
> From: mal hamilton
> Sent: Thursday, January 13, 2011 17:25
> To: rsgb
> Subject: LF: FET RDS
>
>
> LF/MF
> It seems to me if you are working with low V high current FETS the RDS
seems
> reasonable 0.02 for example but when a High V low current device is need
the
> RDS of these devices seem to be around 0.4 considerably higher.
> therefore the efficiency of the amplifier will never reach the 90% plus
that
> some claim.
> I stripped a plasma tv recently and found banks of FETS (6 per bank) and
> wondered why the application neederd so many and have come to the
conclusion
> that because of the high RDS lots were required in parallel to reduce the
> losses.
> Maybe there are low RDS fets about that will handle several hundred volts
at
> modest currents ie 10A at 1000 volts
> Room for thought
>
> de mal/g3kev
>
>
>