Newsgroups: comp.robotics
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From: dwilliam@pizza.ess.harris.com (Dave Williams)
Subject: Re: WHICH H-BRIDGE?
Message-ID: <C5HJ9I.Dr6@jabba.ess.harris.com>
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Organization: Harris Corporation - ISD
References: <1993Apr02.025626.29585@mixcom.com> <1993Apr10.015429.13215@hpcvca.cv.hp.com>
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Date: Wed, 14 Apr 1993 17:58:23 GMT
Lines: 31

In <1993Apr10.015429.13215@hpcvca.cv.hp.com> abrown@hpcvcec.cv.hp.com (Allen Brown) writes:

>If you are running your motor at 5V you can drive it with 74HC240s.
>Just connect lots of them in parallel until you get enough current.
>It sounds crude, but would likely be physically smaller and much
>cheaper than most other solutions.  You could probably use this
>solution down to about 3V.  But running the 74HC240 above 5V would be
>like running your car above redline.  Of course the 74HC240 is much
>cheaper to replace than the engine in your car.

   Wow, now THERE's an angle I hadn't considered before!  Yeesh, that's
definetly not an "intended application" - but it's really neat.

   More info - My Motorola HC logic reference book specs the '240 at
+/- 35 mA per pin.  Each device has 8 output pins, so that's a nice
280 mA per package.  Well, it's probably a pretty crummy 280 mA, since
the '240 is gonna have a voltage drop from hell at that kind of current.
Not to mention that the Icc (supply current) is rated at 75 mA.  In other
words, it isn't gonna be able to disipate the power pulled when all of
the outputs are pushing some heavy current load.  You'd probably fry the 
poor thing under a maxed-out current load.  However, with a few heatsinks 
and a little thermal compound, I'd imagine three or four of them could 
handle most miniture motors quite nicely.

   Hmmmmm...

--
Dave Williams                                   | "What time is it?" "9:00AM"
 dwilliam@jabba.ess.harris.com                  | "What day?"        "Monday"
  "Huh?  What?  Could you repeat the question?" | "Go away.  Try me Tuesday"
    <mumble mumble> opinions <mumble mumble> mine <mumble mumble mumble>
