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[DPRG] Re: Semiconducting Projectiles

Subject: [DPRG] Re: Semiconducting Projectiles
From: David P. Anderson dpa at io.isem.smu.edu
Date: Mon Aug 21 12:29:21 CDT 2000

Howdy


Elliot Johnson wrote:

> I was trying to get a couple of motors working with a TI 754410 H-Bridge
> chip.  I tried hooking it up on a breadboard in a simple circuit, just
> the two power supplies, ground, one motor, and the inputs connected to
> an inverter.  I used a 12V battery connected directly to the motor
> supply and then used a 7805 to power the logic supply.  However, when I
> connected the power to the battery, there was a small crackle and a
> spark shot from the chip about 8-9 inches into the the air and the motor
> didn't even move.  After disconnecting the battery, I found a small hole
> on the top of the chip from the plastic being knocked out.  I've checked
> the circuit for the right voltages, checked all the connections, and
> looked at some others' circuits on the internet.  I can't find anything
> that looks suspicious.  Was it just a defective chip or has anyone else
> run into this problem?  Any help is appreciated, I don't want to ruin
> another one trying to find out if it is a problem with the circuit or
> just a bad part.
> 
> thanks,
> Elliot johnson

I have had a similar experience a few years agao with the Thompson L293
H-bridge.  In my case, I had the polarity of the motor batteries and the
logic batteries reversed.  I hooked up the logic batteries correctly,
tested the CPU, downloaded some code, everything looked ok.  When I hooked
up the motor battery (incorrectly) and powered up, there was, as you
described, "a small crackle and a spark shot from the chip about 8-9
inches into the the air," and released the sacred smoke.

dpa



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