LM317A: Linear regulator supplied backwards

Alexander Elbs

Part Number: LM317A

Hello together,

we use the LM317A to make an output voltage of 5V from 12V.
During the production test, the output of the LM317A will be supplied with 9 V and the regulator input is open (floating).

Is this a problem for the LM317A? Will the regultator maybe even be destroyed or pre-damaged?

Thanks and best regards

Alex

over 7 years ago

0 kai klaas69 over 7 years ago

Guru 140200 points

Hi Alexander,

why not using the protection diode recommended in datasheet?

Kai

0 Alexander Elbs over 7 years ago in reply to kai klaas69

Prodigy 20 points

Hi Kai,

you are right. This can be a solution. I have to choose a diode with max forward drop voltage of 300 mV.
But is this diode really necessary?

Alex

0 kai klaas69 over 7 years ago in reply to Alexander Elbs

Guru 140200 points

Hi Alexander,

I do always use this protection diode. Datasheet recommends the 1N4002 which is fully enough here.

Kai

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LM317A: Linear regulator supplied backwards