UF4004 vs. N4004

[DECKY999]

Is there any advantage using ultra fast 4004 over normal 4004 diodes in linear power supplies? What is the man advantage of MUR860 type diodes over UF4004 variety?

 

[Ouroboros]

The UH400x range have a soft turn-off as well as being fast so they produce a lot less switching noise as a result of the 'snap' turn-off of the reverse currnet that flows for a short time when the diode gets reverse biased. On normal 50/60Hz ac supplies that effect is not normally a problem. (When you get up to SMPSU switching frequencies it is a very different matter!)

 

[Ouroboros]

I meant UF400x range, not UH of course!

 

[DECKY999]

Does that mean that ultra fast and soft switching diodes are simply an overkill for a linear PSU?

 

[Ouroboros]

I have seen simple linear PSUs where there was an issue with EMC (mains conducted noise) which replacement of the 1N540x range devices with UF equivalents solved. It does no harm to use fast, soft-switching diodes at mains frequencies, and might help to keep EMC problems to a minimum.

 

[DECKY999]

That's what I thought as well - thanks. But what about UF4004 against MUR860 or other more expensive fast diodes. Is the higher current rating only advantage?