[sdiy] can a PSU destroy voices chips?

[Jean-Pierre Desrochers]

Hi Neil,

Le 2013-11-19 11:50, Neil Johnson a écrit :
> Hi,
> 
> On 19 November 2013 16:43, Jean-Pierre Desrochers <jpdesroc at oricom.ca> 
> wrote:
>> Sometimes supply regulators in/out pins can get shorted (inside)
>> and cause a too high level at their output pin.
>> I saw 7805 regulators going bad outputing there VDC input
>> (for ex 8-12vdc) at the output pin causing chain reaction...
>> IC's destroyed..
> 
> Except in this case the problem was the positive supply going to 0.
> NOT going above nominal.
> 

I was speaking about terminal IN shorted to terminal OUT
causing the non-regulated high voltage to go at the reg out pin (!!!)

>> The solution... I'm about to try it..
>> just put a transorb in parallel with the regulators output pin
>> to keep the voltage from going above a certain level.
>> Like a 17.1 volts breakdown 1.5KE18AG at the output
>> of a LM7815.
> 
> Carefully read the datasheet of that device.  The 17.1V is the maximum
> working voltage.  The clamp voltage for that device is 25.2 volts.
> 

You are right on that. Sorry I didn't go that far in the transorb 
specs..
The thing was to suggest the transorb clamping technique
to save supply rails from going above a certain level.

JP