Question regarding diodes

[daftpunker]

Hi guys,

I have a problem finding the right diode for my application. I need to put 2 power supplies (different types) in series and need to protect each of them from reverse currents using diodes. I believe that they already have diodes built in, but I want to take precautions.
So my problem is that I am not sure which diodes to order.
One power supply is 52V, 30 Amp and the other one is 30 V, 20 Amp. the circuit will be powered at 72 V and current could increase up to 12.5 Amp.
Since I am not experienced with diodes I am wondering which ones to choose.
I have the following diodes (1N5402), but I believe the current rating does not match.


I found these: http://www.digikey.com/product-detai...ICT-ND/2242770

Do you think they will be appropriate?

Thanks so much

[budm]

Re: Question regarding diodes

If you are going to have 12.5A or more flowing through the Diode, the Vf at that current will be about 1V or more, so at 12.5A, the Diode must be able to dissipate at least 12.5Watts of power. You should get the Diode that can handle at least 25Watts which more likely that it will have to be mounted on the heat sink.

[PeteS in CA]

Re: Question regarding diodes

Maybe I'm missing something, but I think you could use a 60V Schottky, maybe a 20A or 25A rated part (30A or 40A would be even better, but the package might be TO-247 instead of TO-220). That would bring your V(f) down to .6V or .7V, dissipating significantly less power. However you do it, you will need to be able to dissipate a fair amount of power, and heatsinks are not tiny or light.

[daftpunker]

Re: Question regarding diodes

Thanks for the help.
I would like to avoid the use of heatsinks.
Couldn`t I use multiple diodes in parallel? Let`s say 4 diodes rated to 3 A in parallel.
Do you see any problem with this solution?

[budm]

Re: Question regarding diodes

You need room for safety margin, usually x2.

[ben7]

Re: Question regarding diodes

Thanks for the help.
I would like to avoid the use of heatsinks.
Couldn`t I use multiple diodes in parallel? Let`s say 4 diodes rated to 3 A in parallel.
Do you see any problem with this solution?

Well, one might have a lower forward voltage drop than the others, even if it is minuscule, it might make the diode fail (short circuit from over-current) after a while.

[budm]

Re: Question regarding diodes

It is not good to parallel the Diode either unless you use resistors to balance them out or match the Vf really well, the Diode with the lowest Vf will conduct, the one with higher Vf may not conduct at all.

[999999999]

Re: Question regarding diodes

This is a bad design, something is bound to go wrong. Two PSU, different currents, etc.

Can you electrically make something work? Often. Does that make it a good idea? The simplest solution is usually the best one. I may be wrong, you might be stranded on a deserted island with no way to communicate with the outside word or order parts. Otherwise, I hope nothing goes wrong but predict something will, sooner or later...

I'm kidding a little, but not entirely.

[Evil Lurker]

Re: Question regarding diodes

Your looking at three terminal diode type devices, probably one or more STPR1620 ultrafast or BYW series.