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choosing rectifier diodes

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oliver602:
I am trying to choose diodes for a bridge rectifier. I wanted to pick a more general purpose diode instead of one of those 4 pin rectifiers. Something like the 1N400X or 1N540X series.

My question is, What are the trade offs when selecting higher current and higher reverse voltage diodes than necessary?

amspire:
For a mains rectifier operating at 50Hz or 60Hz, there are no major consequences selecting over rated devices. Diodes with a higher current rating will run cooler then lower current diodes anyway which is a good thing.

If you were talking diodes for a switching regulator running at 20kHz plus, then the diode selection is very important as switching losses are a major factor.

Richard

oliver602:
Thanks Richard.

You'd pick the 1000V max reverse voltage if they were cheaper than the 50V version? For a 50Hz rectifier.

amspire:
If the 1000v diode can handle the current, then yes.  It I'd commonly done. 

Back when some of the traditional diodes first came out in the 60s and 70s, they really struggled to make the higher voltages, do it suited them to sell lower voltage version at a much lower price. If you look at the data sheets for the 1n400X range, they all have the same forward voltage drop, so that means they were always trying to make the 1000V 1N4007, but it worked maybe 1% of the time.  All the ones that didn't make the grade became 50v to 800v diodes. Now they can probably make 1N4007s with their eyes shut.

But just double check the spec for the forward voltage drop at the current you are using. If the 50v diode is less, it will run cooler.

Richard

tecman:

--- Quote from: amspire on October 23, 2011, 10:12:55 pm ---For a mains rectifier operating at 50Hz or 60Hz, there are no major consequences selecting over rated devices. Diodes with a higher current rating will run cooler then lower current diodes anyway which is a good thing.
Richard

--- End quote ---

The voltage drop in a diode is the same without respect to the size or current rating.  Therefore the power dissipated will generally be the same.  Larger, higher current rating diodes may appear to run cooler, but this is due primarily to slightly better dissipation of larger leads and diode bodies.

paul

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