parallel connection

if three different voltage sources of 5V, 10V and 15V are connected in parallel, then what will be the voltage across the common point of these sources???

power supplies are designed to output their set voltage at their current limit or whatever current they are capable of supplying . Connecting supplies of different voltages is very much like shorting them to ground. How they respond depends on their configuration, They may have overcurrent protection, in which case they may shutdown. If they are fused it is likely the fuses will blow. They may short out and produce odd noises and smoke, or if you're lucky, flames. Supplies are generally protected from a short much better than they are protected from overrvlotage, so it may be that the lower voltage supplies will be destroyed.

It's possible that (considering only two supplies for simplicity) The 5v supply would just shut off as the voltage was at or above 5v. Then the 15v supply would put out 15v and everyone would be happy. However the 5v supply output parts may not be rated for much more than 5v, and probably not for three times the voltage. The capacitors would swell and bubble or possibly explode. I've seem tantalum capacitors that made a noise like a firecracker and left little black strings in the air. The output over voltage protection (designed to filter short spikes) would be seen as a short to the 15v supply. The spike protection would probably fail, possibly spectacularly, but if the 15v supply has a low current limit it might just pull the 15v supply down. Who knows?

There's no way to tell, from the information you have given. It will be a struggle between supplies that will involve their internal impedances, any current limiting and/or over-voltage protection and other such factors.

But, what the heck, try it and see that happens. But stand back and have a fire extinguisher ready, and if you burn the place down, well, you've been warned ;)

Also, be sure to have a video camera running, that could be YouTube gold!!

And if you want any eyes left afterwards, safety goggles would also be appropriate.

And don't try this at home. Use someone else's home.
Then you'll have a place to sleep tonight.

If voltage source are lab Power supplies than out put will be 15 volt .
How ??
generally DC for power supplly is built by diode or rectifiier bridge
so higer voltage can not flow into the low voltage source as diodes
will be reverse biased. see the attached diagram to understand.

Most power supplies do not have diodes in the output. Bridge rectifiers are used to rectify AC on the input. The diodes have a drop (0.6 to 1v commonly) which affects the output voltage. The drop generates heat which requires a big diode and heat dissipation stuff. If the diode drops 0.6v at 10A that is 6w. Just try and buy a simple 6W diode.

This is the same person who keeps on getting into these discussion disrespecting us all. it's perfectly obvious.

Say what? How did I disrespect anyone, let alone EVERYONE? Did I say anything that wasn't true?. I was just trying to explain in a simple way why the statement was incorrect. Is this forum supposed to let incorrect statements pass for fear of hurting someones feelings? I thought the point was answering questions. How do you see it? Is this a new age forum where there are no wrong answers?

Ididn't say "Are you joking?" which may be an honest response but is not much of an explanation. I don't understand how your answer is respectful and not personal, though I imagine you can enlighten me.

You're making a lot of assumptions about these power supplies. What about regulation? What about switch mode supplies? Hell, he didn't even use the term "power supply". These are "voltage sources". Could be batteries. Could be solar panels -- hell, they could be very talented Electric Eels! Or a mixture, thereof.

Technically this is correct way to achieve this and is a very usefull circuit in UPS, and is actually found in most all laptop PCs.

It on the other hand it's like the old how do you tell the difference between a Norton black box and the Thevenin equal, open circuit? In theory you can't distinguish this two port network unless you are very crafty. Thake both of them, toss them in the snow, the one that melts the snow is the Norton. Norton dissipates power, Thevenin doesn't.

just read the load voltage after the fire goes out... when i was 8 (in the 50;s) i connected a d cell to a 6 volt car battery to see if it would charge.. i still have the scar...