Alt-BEAM Archive
Message #01427
To: beam@corp.sgi.com
From: Terry Newton wtnewton@nc5.infi.net
Date: Wed, 10 Mar 1999 06:23:58
Subject: [alt-beam] Re: Surface mount H-bridge chip
At 11:17 AM 3/10/99 +0100, Steven Bolt wrote:
>On Wed, 10 Mar 1999, Terry Newton wrote:
>> 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)
That'll work but at a cost - it always draws current, even standing
still and if powered up without a driver then poof... for walkers or
something with a switched power supply where the constant drain isn't
a problem, it looks like an easy way to go.
>> 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.
Ouch! .2 volts loss to almost 2 volts... starting at 3 volts
there wouldn't be much left... oh well, better stick with what
I've got, a few hundred ma for a couple ma drive isn't bad.
Terry Newton
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