Greetings guys

I know that this is a bad practice - but do I incur on "burning" any of the power supplies in this situation that I will now describe:

This is an example - hipothetic - but in practice it's what I want to do:

imagine that I have several (different origins) of for example let's say 12V - and one of them comes from a Linear regulator and the other may come from a Switch-Mode Power supply and the other can come let's say from a Car Lighter (and in this last one yes, in this I would use a Diode just to avoid recirculating the 12V from the others to "charge my car's battery")

......they will not be all be "on" at the same time - ALWAYS ONE AT A TIME! - BUT SINCE they all are to power the same device I connect they're outputs all in parallel and as I said I avoid using (a bunch/lots) of diodes (except on the Car lighter's output - I don't want to charge my car's battery

...so the power from the one that is "on" will circulate through the others - (once again, except the car battery. In that one I'll use a diode) - but even the car battery when it is connected to the car lighter (as I said only one at a time will be on) will circulate it's 12V through the Linear and the SPMS power supplies circuitry since they're outputs all connected in parallel.....

Will I burn any of the power supplies?

Thanks!

(EXTRA-PS - from my pratical knowledge the SMPS it's usual when I want to diagnose it to "see what the regulation circuitry is doing by applying a voltage that I increase little by little to see the feedback circuitry working - I do believe that it won't burn up - AND the linear one as long as the polarity is not reversed I do believe that it won't either! - anyway this is really bad practice that's why I ask you guys!

 

Some supplies may tolerate voltage on their outputs when off and some may not.
We'd have to see their schematics to be sure.

 

I would never simply wire the three in parallel, because of the fact that some supplies will emit smoke when they have a voltage connected to their outputs when they are not powered. Those were regulated supplies that fried. With unregulated supplies you might get away with it, but I am not aware of any unregulated switchmode supply types.
So I say don't do it.

 

What is wrong with using a diode for each supply?

 

What is wrong with using a diode for each supply?

Using a diode for isolation makes the system completely different. Diode isolation can work, but be sure the diode forward current ratings are at least 50% over the anticipated current draw,

 

Using a diode for isolation makes the system completely different. Diode isolation can work, but be sure the diode forward current ratings are at least 50% over the anticipated current draw,

.....and take into account the
* voltage drop / power dissipation across the diode
* cooling of the diode if required