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DPRG: H-bridge stuff

Subject: DPRG: H-bridge stuff
From: Jim Brown jimbrown at airmail.net
Date: Fri Jan 2 16:56:42 CST 1998

>Return-Path: <cmcmanis at freegate.com>
>Date: Fri, 02 Jan 1998 14:04:26 -0800
>From: Chuck McManis <cmcmanis at freegate.com>
>Reply-To: cmcmanis at freegate.com
>Organization: Freegate Corporation
>To: jbrown at dprg.org
>Subject: H-bridge stuff
>
>Hi,
>
>Cool bridge design, but a bit complicated. Did you see mine?
>(http://web.professionals.com/~cmcmanis/robotics/h-bridge/h-bridge.html)
>
>I've got a couple of questions.
>
>Why the flyback diodes on the FETs ? The parasitic diode that is built
>into the FET is rated at the same current as the FET and its recovery
>will dominate over the external diode.
>
>Have you read "Power MOSFETs theory and Application" by Gran and Gowar?
>Reccomneded. It gets a bit math intensive but everthing is there. 
>
>Why 1K resistors as pull-ups on the gates? Do you worry about how fast
>you can drive this thing? Given the gate capacitance you could use 47K's
>instead and save your self a juicy current surge.
>
>You're not cross delaying the switch times (that is insuring that a
>change in command from "forward" to "reverse" will delay 1 recovery time
>of the diodes to keep the bridge from having both sides on during that
>time. Do you cover that in the CPU driver or by some other means?
>
>Looks like a great project!
>
>--Chuck
>
>
>
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