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[SOLVED] Positive LDO is (self) destroyed when the output is shorted against negative rail.

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jano2358

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hi!

I making a dual power supply (+-12V) with a pair of DC-DC converters taking feed from 18V brick.
The positive side regulates with a L7987 to 13V and a LDL212 to 12V, I added a bit more of protection with a resistor (1ohm on the test, planed 0.3 later) in series with the LDO, differentiator and comparator, if the compared value rises over the reference the EN pin of LDL212 is shorted.
This works well with overcurrent and short circuit to against GND, but if i short the output against the negative rail, the LDL212 is destroyed even if the EN pin is lowered by the protection.
The datasheet says this device output should not be less than -0.3V and I guess this is the problem, but how I can protect the device from this condition? or is better option to choose other LDO? if yes: any recommendation (less than 0.6V and 1.5A). Thanks!
 

Presume even a lab power supply is not protected against reversed external voltage applied to the output without current limiting. A schottky clamp diode with moderate current capacity (e.g. 3 or 5A) should provide sufficient protection.
 

Hi,

place a schottky diode from GND to OUT.

Klaus
 

Great! I was all the time thinking in a way to protect 'from the positive side perspective' but forcing to be the negative side the one who cuts the energy flow can be a better way. I will try it. Thanks!
 

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