Alt-BEAM Archive
Message #01430
To: beam@corp.sgi.com
From: Steven Bolt sbolt@xs4all.nl
Date: Wed, 10 Mar 1999 14:32:54 +0100 (CET)
Subject: [alt-beam] Re: Surface mount H-bridge chip
On Wed, 10 Mar 1999, Terry Newton wrote:
> >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
Current use is minimal in both `off' states (just a few mA), not
enough to worry about when the subject is a battery powered walker,
or even a battery powered wheeled `bot.
> and if powered up without a driver then poof...
Um, what does `powered up without a driver' mean? I don't see a
`poof' state.
> >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.
Darlington VCEsat in this type of application should be around 0.8V
- far more than the 0.1V to 0.2V of a BC337/327. The trick is to
find plain transistors with a low VCEsat at a low base current.
Given reasonable motors, that isn't too difficult.
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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