Alt-BEAM Archive
Message #02170
To: Martin Labelle beam44@geocities.com
From: John Mitchell johnm@magnet.com
Date: Fri, 9 Apr 1999 15:54:29 -0400
Subject: [alt-beam] Re: H-Bridge
On Thu, 8 Apr 1999, Martin Labelle wrote:
>
> Hi!
>
> For my first Walker I used a 74ALS245 motor driver, and for my next one I
> plan to use H-Bridges.
>
> I found 2 differents shematics on different web sites:
> the first one with 2 PNP transistors and 4 NPN transistors
> and the other one with 4 PNP transistors, 2 NPN transistors and a .47 uF
> capacitor.
>
> Also, I remember that I read someting about a H-Brigde using only 4
> transistors.
>
> So, can someone explain me what are the differences between these
> H-Bridges, like current or other things that are useful to know?
Many H-bridge designs allow a "smoke" state. IE: if your control signals
are (1,1) then Vcc connects to ground, which is **BAD**.
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.)
- j
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