Return-Path: Received: (qmail 15792 invoked from network); 29 Jan 2002 18:24:27 -0000 Content-Transfer-Encoding: 8bit Received: from unknown (HELO warrior.services.quay.plus.net) (212.159.14.227) by exhibition.plus.net with SMTP; 29 Jan 2002 18:24:27 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: (qmail 1143 invoked from network); 29 Jan 2002 18:24:19 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by warrior.services.quay.plus.net with SMTP; 29 Jan 2002 18:24:19 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 16VcqH-00034h-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 29 Jan 2002 18:18:49 +0000 Received: from hestia.herts.ac.uk ([147.197.200.9]) by post.thorcom.com with esmtp (Exim 3.33 #2) id 16VcqG-00034c-00 for rsgb_lf_group@blacksheep.org; Tue, 29 Jan 2002 18:18:48 +0000 Received: from gemini ([147.197.200.44] helo=gemini.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 16VcpT-0001hG-00 for rsgb_lf_group@blacksheep.org; Tue, 29 Jan 2002 18:17:59 +0000 Received: from [147.197.232.252] (helo=rsch-15.herts.ac.uk) by gemini.herts.ac.uk with esmtp (Exim 3.33 #1) id 16VcpS-00030i-00 for rsgb_lf_group@blacksheep.org; Tue, 29 Jan 2002 18:17:59 +0000 Message-ID: <5.1.0.14.0.20020129174706.00abd840@gemini.herts.ac.uk> X-Sender: mj9ar@gemini.herts.ac.uk X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Tue, 29 Jan 2002 18:15:32 +0000 To: rsgb_lf_group@blacksheep.org From: "James Moritz" Subject: Re: LF: PSK31 generation In-reply-to: <3C56CEB5.C52D2542@usa.net> References: <5.1.0.14.0.20020128115929.00ab3b90@gemini.herts.ac.uk> <5.1.0.14.0.20020129144512.02f80bf0@gemini.herts.ac.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: At 17:32 29/01/2002 +0100, you wrote: >I am not familiar with that totem pole scheme, but, isn't it dangerous to >drive a totem pole with 0 degrees ? Wouldn't both the Fet (transistors, >whatever) be brought in conduction state at the same time ? Or is there >a current limiting device ? Just curious... > >73 Alberto I2PHD Dear Alberto, LF Group, "Totem pole" = 2 transistors in series with the top one connected to +ve supply rail, the bottom transistor connected to the -ve rail, and the output taken from the connection between the two transistors; also called complementary push-pull and similar things. Examples are TTL and CMOS outputs, most transistor audio PAs, and of course the Decca PAs The discussion so far relates to a "full bridge" output stage, 2 totem poles with the load connected between the two outputs. As Alberto points out, both transistors in the same totem pole must not be switched on at the same time, or they will short out the supply, called cross-conduction or "shoot through". But provided in one totem pole, transistor 1 is always off while transistor 2 is on, and vice-versa, or both transistors are off, no shoot-through will occur. In the Decca, the two totem poles are always driven 180degrees out of phase from each other. However, the two totem poles could be driven with any relative phase because the impedance of the load limits the possible current flow between the two outputs, and this leaves several possible combinations of duty cycle and relative phase which could be used to vary the power going into the load. Cheers, Jim Moritz 73 de M0BMU