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Old 13th November 2004, 05:30 AM   #1
lopan is offline lopan  United States
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Default 7815

If I tie a 15 or 16 volt source to the output pin of an umpowered 7815 and 0 to its ground pin will this damage it. I want to be able to jump back an forth between two supplies -- one on board and the other outboard.

Any thoughts thanks
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Old 13th November 2004, 02:43 PM   #2
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it might damage the IC...u can put a diode across from the input to the output to solve this problem though...
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Old 13th November 2004, 03:41 PM   #3
dnsey is offline dnsey  United Kingdom
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Why do you need to keep the reg o/p connected when the external supply is in use?
Can't you just switch between them, rather than adding the ext. supply?
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Old 13th November 2004, 04:30 PM   #4
paulb is offline paulb  Canada
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It seems to me that we did some checking once and the 7815 can sink current (it normally sources). It didn't seem to hurt it as long as the current was kept low. So it may work just fine.
They're cheap, so if you blow one up, oh well.
Oh wait, you said unpowered...not sure about that. Try it!
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Old 14th November 2004, 02:19 AM   #5
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u're not suppossed to stick anything after the regulator, and leave the regulator unpowered...check the app note.
www.national.com
the diode thingy I mentioned is in the app note as well
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