Full wave recitifier voltages

[Aether32]

Hi,

When you calculate the voltage rating for a full wave rectifier with filter for a SMPS what method of calculation do you use?

We have a 230Vac input --> 325Vdc from the filter ..

Switching at 450 kHz.

What voltages should we be aware of?

We have just out of spite chosen a 1000V 4A rectifier.. But i would like to find out if there is a method to calculate the peak voltages in this rectifier..

Thank you

 

[Hero999]

Yes, the rectifier just needs to be rated to the peak mains voltage, 400V is normally fine, nothing wrong with 1kV, it's overkill but more is better.

You need to know the minimum voltage the regulator can work from in order to size the filter capacitor.

The safety requirements are tough for exampleto satisfy the safety requirements set by international standards bodies i.e. UL, IEC, IEE etc. for protection against electric shock:

The insulation between the primary and secondary must be able to withstand 3kVAC or 4242VDC without breaking down or arcing.

The creapage distance between the DC rectified mains and secondary side PCB tracks needs to be at least 7mm

There are many other requiremnets you need to fulfil, I only mentioned the most important ones as someone else here had designed a dangerous PCB which didn't fulfill any of the above.

 

[indulis]

...the rectifier just needs to be rated to the peak mains voltage,

Hmmm... wouldn't it be the input voltage plus the rectified voltage. The "output" would peak charge to 325VDC, but when the input swings negative the diode will have twice that voltage across it.

 

[Hero999]

For a single rectifier yes, but no, not, for a bridge, don't forget there are two diodes so the breakdown voltage is higher.

 

[Aether32]

Great, thanks!