Alt-BEAM Archive

Message #10737



To: beam@sgiblab.sgi.com
From: Victor Snesarev snesarev@ecel.ufl.edu
Date: Wed, 23 Feb 2000 08:57:13 -0500
Subject: [alt-beam] Re: Walker problems


I'm not up on the H-bridge circuit, but the following might give you an
idea:

http://mil.ufl.edu/imdl/handouts/Motor_Driver1.pdf

This circuit uses relays to switch the motor on and high power darlington
transistors to drive them. I was told that the relays in the circuit are
rated at 5Amps with 12-V coils, and that transistors Q3 & Q4 are used to
step up the voltage from 5V. I was also told that you can order 5A DPDT
relays with 5-V coils from Digikey.

Darlington pair transistors can be substituted with power MOSFETs to get
more current.

It is a good idea to connect a diode across the relay to avoid back-EMF
current from destroying your circuit, but I'm not sure what kind of diode
is needed, so ask the list if you ever get to building the circuit.

Oh, and then there are commercial H-bridges available in chip form like
this one rated at 3A, 55V, for example:

http://www.national.com/pf/LM/LMD18200.html

Just my 2 cents.

Victor


Bruce Robinson wrote:

> Jim Taylor wrote:
> >
> > Is thier a schematic avalible for an H-bridge, that could
> > handle up to say 5 amps?
>
> umm ... What in HECK are you going to shove around with that kind of
> current, Jim?
>
> The H-bridge circuit I use is a 6 transistor job that uses a pair of
> low-power, general purpose transistors (2N3906 or 2N3904) to drive 4
> other transistors. I've successfully used transistors up to 800 mA for
> the 4 "others", but I don't know for sure that you could go up to 5
> amps.
>
> I'll look into it a bit. Meanwhile, anyone else out there ....?
>
> Bruce

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