What happens with rectifier diodes at high frequency?

[codex653]

i've always wondered what would happen if you used rectifier diodes in a switchmode supply! i'm building 2 switchmodes and i'm curious what would the result be if i used them....now i'm NOT going to officially use them in the smps, i just want to know what would happen.
anything "spectacular"? hehe

 

[crutschow]

Nothing "spectacular". After conducting in the forward direction, standard junction rectifier diodes have a long reverse recovery time of perhaps a few microseconds when you apply a reverse voltage (they will conduct in reverse direction for a short period of time). This is of no consequence at power line frequencies but it creates significant loss at the high frequencies that switchmode supplies use. That is why fast reverse-recovery diodes, typically Schottky, are used in switchmode supplies.

 

[codex653]

ahh ok...oh well, i was hoping something cool would happen so there is just heat dissipation..that's boring!

 

[audioguru]

"Something cool" happens in cartoons, not in real life.

Although a big electrolytic capacitor connected backwards to a high current power supply produces a "cool" spectacular explosion.

 

[codex653]

hahahaha yes it does audioguru, yes it does i did that once from a good distance of about 50ft with a plastic shield/face mask on just incase of any debris...oh that was fun!

 

[Nigel Goodwin]

ahh ok...oh well, i was hoping something cool would happen so there is just heat dissipation..that's boring!

The rectifiers will simply rapidly overheat, and then go S/C - hopefully, if your supply is correctly designed, nothing spectacular would happen.

 

[codex653]

yah i'm gonna be using some 40v 1A Schottky diodes in parallel...i have a 30v output from the switchmode and pretty much a guaranteed 3A average current draw and around probably 6A peak, so i get to use lots of diodes hahaha


EDIT: oh, and a heatsink just in case

 

[ronv]

You are a funny guy!
1 amp diodes in parallel with a big heatsink.

 

[Roff]

yah i'm gonna be using some 40v 1A Schottky diodes in parallel...i have a 30v output from the switchmode and pretty much a guaranteed 3A average current draw and around probably 6A peak, so i get to use lots of diodes hahaha


EDIT: oh, and a heatsink just in case

You might need series resistors to prevent thermal runaway. Why not just use rectifiers that are rated for the application?

 

[codex653]

thanks ronv! haha

-Roff...exactly what i was thinking too about the runaway... as for the correct ratings, problem is that i was ordering all of my parts from a single website so that i could get combined shipping, and they didn't really have any schottky diodes that were rated above 1A and 40v :/ and for the price i got them, it would have cost more when buying from another place with the shipping included....so i guess it's just a trade off ...BUT! i did find a 40v 10A Schottky diode today in my parts bin!!! im so happy! that takes away atleast SOME of the problem )

 

[CRISespecialist]

i suggest for me,that i must look carefully with the rated voltage and compute what im going to use rectifier diode that closely,so that it would not burn out any other component like cap,that can cause fire or enjury.

 

[Sceadwian]

Why would you parallel that many 1amp diodes? Buy bigger rectifier diodes, they're not that expensive, maybe 50-75 cents each for 6 amp rated diodes.

 

[#12]

Scead, see post #10