Alt-BEAM Archive
Message #02186
To: beam beam@corp.sgi.com, Martin Labelle beam44@geocities.com
From: "Ben Hitchcock" beh01@uow.edu.au
Date: Sat, 10 Apr 1999 15:32:29 +0000
Subject: [alt-beam] Re: H-Bridge
>The 6-transistor version makes this state go away, which is good. Or, you
>can add two resistors and wind up with the enclosed diagram from Ben
>Hitchcock. (I've built this circuit, and it either only works up to
>~200mA, or I'm an idiot. Leaning towards #2, but just a FYI.)
>
You need to use transistors that can handle the current (obviously!), and
you also need to give them enough base current for them to work properly.
For example, if I were to use a transistor with a gain of 100, I would need
to give it at least 2 mA of base current to get 200 mA flowing in the motor.
Since most 74HC chips don't give out more than a few mA, you're better off
finding a transistor that has a high gain with also a high current
capability.
None of my robots need 200 mA, so I'm pretty safe with my BC337 and BC327's.
Ben
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