Alt-BEAM Archive
Message #01425
To: beam@corp.sgi.com
From: Steven Bolt sbolt@xs4all.nl
Date: Wed, 10 Mar 1999 11:17:50 +0100 (CET)
Subject: [alt-beam] Re: Surface mount H-bridge chip
On Wed, 10 Mar 1999, Terry Newton wrote:
> Actually, the transistors inside have sufficient gain by themselves,
> no additional transistors are needed if the driving circuit can tolerate
> about a 1.5K load, good for a few hundred milliamps. Not an emitter
> follower but a 4 transistor H-bridge. Ascii ahead use fixed font...
>
> Zetex Active-Low H-bridge 11 = off 01 = goes one way
> ------------------------- 00 = poof 10 = goes the other way
---8<---
> Making 'em non-smoking takes more resistors and diodes,
> for the Active Low design, connect..
>
> .----------|<|------< from Out B of bridge
> In A >---1K--*---470------> to In A of bridge
> .----------|<|------< from Out A of bridge
> In B >---1K--*---470------> to In B of bridge
>
> Diodes = 1N34 or 1N914/4148 (pick for low forward if possible)
> For the Active-High design - turn the diodes around.
Actually, a non-smoking version doesn't need extra parts. You can
do it like this:
http://www.xs4all.nl/~sbolt/Other/Hsmt-bridge.gif
(7961 bytes)
I've drawn 74HC schmitt-triggers to provide base current to the
bridge; that's the kind of output you would normally be amplifying,
so I don't count them as extra parts :)
---8<---
> I noticed a jewel - the Zetex 6702 with darlington transistors, same
> circuit but the resistors can be much larger, 10K or more.
But a darlington comes with a much higher VCEsat, and large voltage
drops in series with the motor are not a good idea at our usually
low supply voltages.
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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