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DPRG: DPRG project

Subject: DPRG: DPRG project
From: Jim Brown jimbrown at airmail.net
Date: Thu Jan 1 15:16:56 CST 1998

>Return-Path: <geo at z9.com>
>X-Sender: geo at ami.z9.com
>Date: Thu, 01 Jan 1998 07:52:52 -0800
>To: jbrown at dprg.org
>From: George Pontis <geo at z9.com>
>Subject: DPRG project
>X-MDaemon-Deliver-To: jbrown at dprg.org
>
>Hi Jim,
>
>I just came across your site after seeing a reference to it on a Coldfire
>mailing list. It was interesting to look at the schematic, since this I
>have some experience in this area.
>
>The driver section is really the hardest part of the design, in my opinion.
>May I suggest that you consider making some improvements in the MOSFET
>driver section to improve efficiency and performance. While your circuit
>will work fine at lower switching speeds, the slow turn-on of the MOSFETS
>will interfere with efficiency. The 7438 is not strong enough to turn the
>MOSFETS off quickly, which is the next limit that you might encounter if
>you go to lower value pull-ups. Some sort of active push-pull drive would
>solve that problem. It is unfortunate that there is not a simple way to
>implement push-pull drive using everyday parts. However, there are IC
>drivers made by I.R. and Linear Technology that work very well and offer a
>number of additional features. For one, they implement current limiting for
>transistor protection. Also, they are usually set up to drive two N-channel
>MOSFETS.
>
>A second issue is that you really would like to be able to chop a stepper
>motor with the highest practical voltage, unless you are never going to
>turn it fast. As the speed goes up, the higher voltages are needed to
>overcome the motor inductance and maintain the desired winding current. If
>the current trails off, then the high speed torque of the motor is reduced.
>If your design would be capable of working at 24V or more, it would be that
>much better for high speed operation.
>
>Best wishes,
>
>George Pontis
>
>
>
>
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