Parallel multiple secondary diodes - why ?

[genuineguy]

Dear Experts
I have seen that many SMPS circuits have parallel connected ( yes, physically different but parallel on the board)schottky diodes. There must be a reason for the same. I tried to search on google but could not get a technical explanation. Could you please help with the theory or some link to a document that describes the same ? I have a feeling that its got to do with something from snubber perspective and not just increasing current capacity

[dick_barton]

Re: Parallel multiple secondary diodes - why ?

They share the current flow. If one diode was rated for 1 amp then paralleling 2 diodes allows for 2 amps to flow. 1 amp per diode.
The only problem with this is that if they are run close to their maximum current rating, failure often results after a while.

[genuineguy]

Re: Parallel multiple secondary diodes - why ?

Thanks dick_barton.
Going forward, I will address all as members and avoid using the word experts

The circuit I am dealing with has 4 in parallel. Interestingly there is no RC snubber or any free wheeling diode at the secondary side. I am still struggling to see why its not affecting the primary side ( blow the mosfet) without the same

[mariushm]

Re: Parallel multiple secondary diodes - why ?

It's also to lower voltage drop on each diode and may also be for heat dissipation...

For example, the diode may have 0.35v drop at 1A but only 0.15v at 0.25A ... so put 4 in parallel to get only 0.15v drop on them instead of a full 0.35v

0.35v drop x 1A = 0.35w dissipated on a diode ... or you can have 0.15v x 0.25a = 0.0375 w per diode ... or 0.15w dissipated over 4 times the surface, and with 4 times as many leads dissipating heat through the pcb traces as well.

[CapLeaker]

Re: Parallel multiple secondary diodes - why ?

Can we see some pictures?