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why did my regulator blow up

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amateur_25:
Thermal limiting if pushed can the regulator blow up and produce a spark across the terminals
or have shorted somthing out? Correct me if wrong the 7805cv has both thermal and output protection?

Psi:

--- Quote from: amateur_25 on April 03, 2012, 12:33:44 pm ---Thermal limiting if pushed can the regulator blow up and produce a spark across the terminals
or have shorted somthing out? Correct me if wrong the 7805cv has both thermal and output protection?

--- End quote ---

The 78xx/79xx series has both current and thermal limiting but you can still blow them up.

One way to kill them is to push their output higher than the input (using some other power source).
Also an overly large capacitor on the output can do it too, as it will feed backwards when the input power is turned off.

Mechatrommer:

--- Quote from: Psi on April 03, 2012, 12:39:59 pm ---Also an overly large capacitor on the output can do it too, as it will feed backwards when the input power is turned off.

--- End quote ---
i think thats why datasheet recommends the reverse diode between output and input and its drawn as BIG diode.

amspire:

--- Quote from: amateur_25 on April 03, 2012, 12:33:44 pm ---Thermal limiting if pushed can the regulator blow up and produce a spark across the terminals
or have shorted something out? Correct me if wrong the 7805cv has both thermal and output protection?

--- End quote ---

Also the thermal limiting in these regulators is only designed for allowing the regulator to survive a short term overload. It is not designed for regular use, as when it is in thermal limiting, the junction temperature can be 10 degrees above the absolute maximum junction temperature. I wouldn't bank on a 7805 lasting too long if it was regularly taken into thermal limiting.

If you wanted a reliable design, and say you wanted to get 1A from the 7805, the maximum input voltage I would allow for a TO220 package device would be 13V if it was on a big external heatsink or 8V if it was on a PCB heatsink. If there is no heatsink, you cannot run a 7805 reliably at 1A output. 400mA max with 8V input perhaps.

If I was regularly going to overload or short out the 7805, I would add an extra current limit circuit before the regulator, or use a different regulator with a proper current limit.

Richard.

amateur_25:
I've always used 100uF on the input and 10uF on output. is this ok?

Could you explain what u mean by proper protection?

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