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Stupid Bridge/Diode Question
Stupid Bridge/Diode Question
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Old 7th February 2006, 07:58 PM   #1
richie00boy is offline richie00boy  United Kingdom
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Stupid Bridge/Diode Question
Default Stupid Bridge/Diode Question

If I build a discrete bridge rectifier using 4x 100V diodes, is the bridge rectifier as a whole rated to 200V?
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Old 7th February 2006, 08:09 PM   #2
anatech is offline anatech  Canada
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Stupid Bridge/Diode Question
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.

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Old 7th February 2006, 08:26 PM   #3
richie00boy is offline richie00boy  United Kingdom
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Stupid Bridge/Diode Question
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.
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Old 7th February 2006, 09:26 PM   #4
peranders is offline peranders  Sweden
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Stupid Bridge/Diode Question
45 VAC and 100 V diodes is a bit weak. 200 V at least. You must also have incoming voltage transients in mind.
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Old 8th February 2006, 07:33 AM   #5
richie00boy is offline richie00boy  United Kingdom
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Stupid Bridge/Diode Question
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.
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Old 8th February 2006, 07:39 AM   #6
moamps is offline moamps  Croatia
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Quote:
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.

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Milan
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Old 8th February 2006, 08:09 AM   #7
richie00boy is offline richie00boy  United Kingdom
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Stupid Bridge/Diode Question
Thank you, that is the kind of answer I was looking for.
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Old 8th February 2006, 08:26 AM   #8
richie00boy is offline richie00boy  United Kingdom
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Stupid Bridge/Diode Question
So what about half wave voltage doublers? I used 60V diodes on a scheme similar to this

Click the image to open in full size.
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.
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Old 8th February 2006, 09:31 AM   #9
AndrewT is offline AndrewT  Scotland
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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?
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Old 8th February 2006, 10:04 AM   #10
Nigel Goodwin is offline Nigel Goodwin  England
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Quote:
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.
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