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From: seeker@indirect.com (Stan Eker)
Subject: Re: Source for L293B ICs?
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Date: Sun, 21 May 1995 03:40:34 GMT
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Bruce "Honkin' Blues Monster" Ediger (bae@ssds.com) posed:

: Richard Hughes was kind enough to put togther a mass purchase of L293D
: integrated circuits.  Now that I'm almost done with my 6.270 board kit,
: I find that I have 4 L293Ds, where the assembly calls for 2 Ds and 2 Bs.

: Where can I find L293Bs?  Digi-Key doesn't appear to carry them, and the
: two best part stores in the Denver, Colorado area don't carry them.

: Anybody got suggestions?

Not in the hobby distribution channel.  If you know anyone there that works
for a small electronics firm, they can get 'em out of commercial disties,
either the original L293B or one of the ones below from the FAQ:

> The L293D, motor driver on a chip, is an SGS-Thomson part and is
> second sourced by Unitrode. In spite of its utility it is not readily
> available in small quantities. This part is a dual full H-bridge that
> can drive motors up to 0.6A.

> The significance of the 'D' in L293D is that it is diode protected.
> There is a reverse biased diode that shunts the reverse EMF from a
> motor to the V+ supply. The L293B doesn't have this diode so it must
> be provided externally.

> National has an LM18293 which they say is a cross for an L293B. The
> price should $4.00 or less and they need the external diodes. A
> replacement for the D part is the Texas Instruments 754410 which
> actually has a bit better current capacity (1A vs .6A) this latter
> part is available from Arrow electronics in the US.

> An alternative part is the UDN2998. This is a 3A bridge in an inline
> package, it is limited to motor supplies greater than 10V. You can
> also build your own H-bridge out of either bipolar chips or MOSFETs.

The last line makes the most sense.  You can easily go over the 1.6A rating
of the L293B + L293D by stalling many hobby motors.  The total cost of doing
a bipolar H-bridge good for a few amps is about the same as the SGS combo,
and less likely to smoke if you hit a wall.  The MOSFET route is about 3-4
times as expensive, but you can hit currents of 20A or more, and they'll
handle lower drive voltages than the 6-10 most bipolar units need.

