Ben L Wirz wrote:

>         You have used the L293D or the L293 to 1 Amp?  The L293 is rated
> at .6 A and the L293D is rated at 1 Amp, or they can be bridged for
> double capicity.  Can I also ask where you found the L293's if thats what
> you used, I haven't been able to find them in anything less then 200 min
> order.

I'm afraid you should not try to increase the current capacity by
paralleling outputs of bipolar devices, such as the 293. If you do,
the maximum allowable current will be not be the sum, but the minimum
of the individual maxima.

The reason is as follows:

Bipolar transistors have negative temperature coefficient,
i.e. resistance goes down as they heat up. For two paralleled outputs,
the one with lower on-resistance will take more current, and will heat
up more, resistance becomes even lower, etc. The positive feedback
quickly causes current imbalance.

MOSFETs are different, and have positive temperature coefficient, so
from this point of view, their outputs can be paralleled. However,
there can be other problems with paralleling MOSFETs.

I have heard quite a number of reports of people blowing up their 293s
by paralleling outputs, many of them from builders of the 6.270 board,
where the assembly manual at one point suggested piggy-backing of two
293s.

Martin Nilsson                           http://www.sics.se/~mn/
Swedish Institute of Computer Science    E-mail: mn@sics.se
Box 1263, S-164 28 Kista                 Fax: +46-8-751-7230
Sweden                                   Tel: +46-8-752-1574