Burned up my first chip!

[David Chambers]

Joe Boucher wrote:
> 
> 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
One other thing you need to check is that if you run long input or
output leads. ie > 6" you will need a small cap right on the input pins
of the regulator. Say 10uf at 35V. It is also good practice to put the
same size and value cap on the 5V output as well. These caps stop the
7805 oscillating and cooking itself.
David Chambers