Return-Path: Received: (qmail 24071 invoked from network); 31 May 2001 07:38:39 -0000 Received: from unknown (HELO warrior-inbound.servers.plus.net) (212.159.14.227) by excalibur.plus.net with SMTP; 31 May 2001 07:38:39 -0000 Received: (qmail 16184 invoked from network); 31 May 2001 07:38:12 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by warrior with SMTP; 31 May 2001 07:38:12 -0000 Content-Transfer-Encoding: 8bit Received: from majordom by post.thorcom.com with local (Exim 3.16 #2) id 155Mv1-00080w-00 for rsgb_lf_group-outgoing@blacksheep.org; Thu, 31 May 2001 08:30:55 +0100 Received: from bob.dera.gov.uk ([192.5.29.90]) by post.thorcom.com with esmtp (Exim 3.16 #2) id 155Mux-00080r-00 for rsgb_lf_group@blacksheep.org; Thu, 31 May 2001 08:30:51 +0100 X-Priority: 3 X-MSMail-Priority: Normal Received: by bob.dera.gov.uk; (8.8.8/1.3/10May95) id IAA31099; Thu, 31 May 2001 08:34:36 +0100 (BST) Received: (qmail 29088 invoked from network); 31 May 2001 08:23:59 -0000 Received: from gauntlet.mail.dera.gov.uk (172.16.9.10) by baton.dera.gov.uk with SMTP; 31 May 2001 08:23:59 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: by gauntlet.mail.dera.gov.uk; id IAA09909; Thu, 31 May 2001 08:16:41 GMT Received: from unknown(10.71.64.31) by gauntlet.mail.dera.gov.uk via smap (3.2) id xma009822; Thu, 31 May 01 08:16:06 GMT Received: from mailex.dera.gov.uk (unverified) by mailguard.dera.gov.uk (Content Technologies SMTPRS 4.1.5) with SMTP id for ; Thu, 31 May 2001 08:38:02 +0100 Received: (qmail 16495 invoked from network); 31 May 2001 07:20:43 +0100 Received: from softdnserror (HELO cchecker.dstl.gov.uk) (192.168.248.52) by 10.10.80.250 with SMTP; 31 May 2001 06:20:43 -0000 Received: from FRN-MAIL-R1.dstl.gov.uk (unverified) by cchecker.dstl.gov.uk (Content Technologies SMTPRS 4.1.2) with ESMTP id for ; Thu, 31 May 2001 07:20:48 +0100 Received: by frn-mail-r1.dstl.gov.uk with Internet Mail Service (5.5.2650.21) id ; Thu, 31 May 2001 08:28:53 +0100 Message-ID: <7D653C9C42F5D411A27C00508BF8803D55C4A5@pdw-mail-r1.dstl.gov.uk> From: "Talbot Andrew" To: rsgb_lf_group@blacksheep.org Subject: RE: LF: Field effect versus bipolar tran sistors Date: Thu, 31 May 2001 08:28:54 +0100 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2650.21) Content-Type: text/plain; charset=iso-8859-1; format=flowed Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: That centre tapped coil in the Decca transmitters is there to 'soak up' high current pulses generated in the short switching interval when both FETs may be on together - a few ns duration. This comes about since the turn-off time of power FETs is of longer duration than the switch on time. The 15 ohm resistor across the coil is the damping to prevent high frequency spurious oscillations. In a SMPSU the there is a deliberate dead band generated at the cross over, when both devices in a push pull pair are switched off, but this is undesirable in a very high efficiency class E transmitter. Andy G4JNT > protective means > against this. The centre tapped coil for instance, loaded by > 15 ohms, located > between both power FETs in the Decca 5501 PA output, seems to > me to be such a > protective device. > > In a certain way, my complementary bipolar PA is even showing > similarities to > this basic Decca power amplifier block mentioned, such as two > transistors in a > totem pole configuration, the output employing a series > resonant circuit . . . > > 73 Ha-Jo, DJ1ZB> -- The Information contained in this E-Mail and any subsequent correspondence is private and is intended solely for the intended recipient(s). For those other than the recipient any disclosure, copying, distribution, or any action taken or omitted to be taken in reliance on such information is prohibited and may be unlawful.