# PIV in rectifier

Discussion in 'General Electronics Chat' started by harikanaidu, Mar 9, 2015.

1. ### harikanaidu Thread Starter Member

Nov 28, 2014
76
1
Why the peak inverse value of a full wave rectifier is 2vm.....As i know peak inverse value is the maximum voltage that a diode can resist in reverse bias

2. ### Hypatia's Protege Distinguished Member

Mar 1, 2015
2,850
1,317
Under reverse bias, a rectifier diode must withstand the absolute value of the peak (inverse) supply EMF plus, the charge on the filter (hence 2*peak supply EMF) --- That said I'm not certain I understand your question inasmuch as these considerations are not typically applicable to bridge rectifiers...

Are you referring to a taped secondary arrangement? (in which case, for reasons similar to those discussed above, the rectifiers must withstand twice the output EMF)

Best regards
HP

Last edited: Mar 9, 2015
3. ### harikanaidu Thread Starter Member

Nov 28, 2014
76
1
yes i am reffering to tapped secondary arrangement.

4. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,159
772
Piv on diodes is twice the maximum AC voltage,so if your rectifying say 230V, you need a piv of 500v to be safe.

planeguy67 likes this.
5. ### Hypatia's Protege Distinguished Member

Mar 1, 2015
2,850
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A taped secondary scheme may be viewed as a pair of 'tandem' half-wave rectifiers (each side of the tap) -- bearing that in mind please refer to the opening paragraph of my initial post on this thread...

Best regards
HP

Last edited: Mar 9, 2015
6. ### ian field Distinguished Member

Oct 27, 2012
4,459
792
With no load; the reservoir capacitor will charge to the AC peak value, so the rectifier must withstand that plus the AC peak value when it swings the other way.

Don't forget to allow a safety margin to cope with any mains borne transients, you can put up to about 10nF in parallel with the diode to help damp out spikes - another valid approach is to clamp the input with a metal oxide varistor.

7. ### ian field Distinguished Member

Oct 27, 2012
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792
PC monitors supplied for the UK system usuall came with at least 600V PIV bridge rectifiers, many had 800V types. Of course a bridge rectifier has 2 diodes in series at any one time - so the actual withstand was 1200 to 1600V.

Presumably this includes a margin to survive mains transients - but most manufacturers also included spike damping capacitors in parallel with each diode and/or a MOV on the mains input.

8. ### #12 Expert

Nov 30, 2010
16,704
7,354
Ahh... 2 x Vmax.
For a moment I though you were chasing a typo that said, "2 millivolts".