On Jun 30, 2005, at 3:18 PM, Russell McMahon wrote:

>> Why not parallel a boat load of opposing 74AC04's or some other 
>> equivalent beefy driver?

> Another potentially useful idea that alas isn't quite up to my 
> requirement.
>
> There may be another family that would do better.

There are some micro RC circuits that are using op-amps as H-bridge
drivers.  I was surprised, but apparently some rail-rail opamps have
surprisingly high current capabilities.  The MAX4020 has 4 opamps
and drives +/-120mA;
http://www.oyajin.jp/~toko/pic/0038/index.html  (japanese, but the 
schematics
    are readable and the pictures are amazing.)
http://www.geocities.com/billy8601/infraredray/diy-ir.html

Audio amps are another possibility.  the BEAM robotics people have
used LM386 amps as motor drivers in a number of applications.

(I suspect that at 4V supply, your sorta-darlington configuration
suffers a lot from the inherent high Vcesat of a darlingtons.  You
could be looking at as much as 1.2V on each side of the load, right?
(I'm not sure both sides are exactly darlingtons...)  If that's the
case, you could get some major benefit by replacing the input 
transistors
with fets?)

BillW

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