Burned up my first chip!

[BUTLER, Tom]

Those 7805 regulators are pretty rugged devices.  Shorting the output
isn't a good thing to do, but should not cook it.  Those things are
supposed to have thermal overload protection.  You're right...35 volts
IS the maximum input.  You should give the 78XX devices about 3 volts or
mor above the regulated voltage as input.  There are only two things I
can think of which might have smoked your regulator.  First, it may have
been defective.  Second, was that 12V DC and was the polarity correct???
Tom Butler

> -----Original Message-----
> From:	Joe Boucher [SMTP:BoucherJC at lmtas.lmco.com]
> Sent:	Monday, January 26, 1998 11:24 AM
> To:	diy_efi at efi332.eng.ohio-state.edu
> Subject:	Burned up my first chip!
> 
> I was playing around in the garage Sunday before THE GAME setting up a
> power supply from an old modem to test some of the circuits you guys
> and
> girls have come up with.  I was curious about a 7805 votage regulator
> I
> bought at Rat Shack.  The back of the card said the input voltage was
> 35
> volts.  I thought that probably meant max voltage so I hooked up a 12
> volt power supply to it.  I was getting 5 volts out of it when it
> started smelling funny and a small spot on the chip started bubbling.
> 
> Ooops.
> 
> I think I shorted two of the leads coming out of the chip with the
> voltmeter probes.  1) Did that do it? 2) Inputing 12 volts didn't do
> it,
> did it?  3) Did having no load do it?  4) Does it need a heat sink
> which
> is why the back side was nice and shiney?
> 
> I found a store near me that sells 6000 types of chips and surplus
> parts
> for a lot less than Rat Shack.  But the hours are inconvenient and the
> owner is a jerk.  Can't have everything.
> 
> Joe Boucher
> '70 RS/SS Camaro  '81 TBI Suburban