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Electronics => Projects, Designs, and Technical Stuff => Topic started by: johnnyfp on August 21, 2013, 05:13:54 am

Title: Damaging a LDO through powering the Ouput?
Post by: johnnyfp on August 21, 2013, 05:13:54 am

I put togetherthis circuit (http://goo.gl/9qr8y) that has a Microchip which I program from a PicKit3. I've setup the Pickit3 to supply 3.3v power when programming.

My question is, will power on the output but not the input damage the LDO? I'm using a Micrel 5219 (http://www.micrel.com/index.php/en/products/power-management-ics/ldos/single-ldos/article/85-mic5219.html) and can't see anywhere in the datasheet if powering the LDO thorough the output will damage it or if I need to add a diode to protect it.

I can recall somewhere that doing so does in fact damage it. Reason I'm asking is that now the LDO is only supplying 2.7v instead of the expect 3.3v which tends to lead to the conclusion that it indeed does damage the LDO if 3.3v is present on the Output but nothing on the input.

Cheers

Title: Re: Damaging a LDO through powering the Ouput?
Post by: hlavac on August 22, 2013, 06:37:58 am

It is quite common for linear regulator pass transistor to be damaged by reverse current from output to large input filtering cap, or by negative voltage. A few regulators have built in protection for that but not many.

You are supposed to put one reverse diode across the output and another across the regulator back to the input cap to protect the regulator.