7805 abuse

LoopyByteloose

What happens when you properly ground a 7805, but apply +12v to both the input and output?

No damage or disaster? I have this soldered in place and it seems broken, but I'd like to confirm the damage as I may destroy the 7805 during removal [noparse][[/noparse]it is easier to cut the leads and then clean up the board].

I do know that backflow from larger capacitors does damage a 7805, so I am presuming the latter. I now get 9.45 volts in and 9.45 volts out.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Ain't gadetry a wonderful thing?

aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan

LoopyByteloose

Seems I locally purchased a batch of 5 broken regulators. None of them do anything. At least I am cautious enough to verify the right voltage and no shorts before plugging in other components.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Ain't gadetry a wonderful thing?

aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan

kwinn

Loopy, I have a simple circuit for testing 78/7900 series regulators before I solder them in. Two 47 ohm resistors, 4 small caps, and a 6 pin connector. 78xx goes in pins 1-3, 79xx in pins 4-6, connect to supply and measure output voltage. Checking takes a minute or two from start to finish.

Prettybird

78xx series voltage regulators are pretty tough but it sounds mabe fried. Properly heat sinked acording to specs. they can 1.5 amps. They automaticly shut down when short circuitted. The most dangerous situation is running close to the limit before shutdown. I think the 12v on the output fried the protection circuitry. I have seldom seen a bad one when a bench technician years ago.

sam_sam_sam

The data sheet are very clear with way is input and which is output

If it shows the out line of the metal tab then you look at it from that side

When you have 78xx laying flat it right side is the output side and the left side is the Input side and the center lead is VSS



▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
··Thanks for any··that you may have and all of your time finding them

·
·
·
·
Sam