Stupid Bridge/Diode Question

[richie00boy]

If I build a discrete bridge rectifier using 4x 100V diodes, is the bridge rectifier as a whole rated to 200V?

[anatech]

Hi richie00boy,
I would think 100V. It is reverse biased on alternate cycles with one end being the rectified voltage close to peak, the opposite goes the other way.

-Chris

[richie00boy]

Yes, but the current has to pass through two diodes on the journey. I an interested in the theoretical answer but also from a practical viewpoint as I currently have a bridge made from 100V diodes running off a 45VAC winding and has been given some abuse without blowing.

[peranders]

45 VAC and 100 V diodes is a bit weak. 200 V at least. You must also have incoming voltage transients in mind.

[richie00boy]

Yes but from a purely theoretical view, is a bridge made from 100V diodes rated to 200V?

As 45V * 1.414 = 63V which when doubled to take into account of reverse bias bridge gives 126V yet my bridge has not blown up.

[moamps]

Originally posted by richie00boy
As 45V * 1.414 = 63V which when doubled to take into account of reverse bias bridge gives 126V yet my bridge has not blown up. [/B]

No.
Reverse voltage on each diode is Vpeak-Vdiode(on)=ca Vpeak
like Chris already said.

Regards,
Milan

[richie00boy]

Thank you, that is the kind of answer I was looking for.

[richie00boy]

So what about half wave voltage doublers? I used 60V diodes on a scheme similar to this


Schematic copyright Rod Elliot, sound.au.com

but they blew up with an 18V transformer. Yet 18*2*1.141=51V which should be within their capabilities.

[AndrewT]

Hi,
a bit off topic but why on earth are you feeding 51Vdc into a 7815/7915? They are almost certain to blow. With or without a load on the end. Or is your circuit only delivering 25Vdc to each?

So back to topic

Is a 4 by 100V diode bridge equivalent to 100V or 200V PIV?

[Nigel Goodwin]

Originally posted by AndrewT

Is a 4 by 100V diode bridge equivalent to 100V or 200V PIV?

Interesting question!

In theory it would be 200V, as the two diodes are effectively in series in each side of the bridge. BUT!, there's no voltage sharing resistors across them, so they won't be accurately balanced - so it will be greater than 100V but less than 200V (the exact value depending on the exact spec of the individual diodes).

Personally, I'd still rate it as a 100V bridge, if you want 200V, then use better diodes! - the price difference is pretty insignificant.