Bridge rectifier connected in parallel

[terrycyk1981]

Dear all,

Does anybody tell me what is the purpose of constructing a bridge rectifier in parallel?

The Input is 230 AC voltage and pass through 2 bridge rectifier which constructed in parallel and output is 24 DC voltage

 

[Nigel Goodwin]

To double the current capacity.

 

[deepak george]

just to increase the current capacity....probably those diodes used cannot handle the output current....hence they had to use two bridges in parallel

 

[Arkham00]

I'm not sure ... I know you cannot parallel diodes and I suppose you cannot parallel bridges too ...

 

[Nigel Goodwin]

I'm not sure ... I know you cannot parallel diodes and I suppose you cannot parallel bridges too ...

You 'know' incorrectly, although it's not recommended to parallel diodes (unless you fit current balancing resistors in series with them) it is common commercial practice to do so.

Likewise, paralleling bridges is no different, and probably slightly better, as you have two diodes in series at all times.

 

[Arkham00]

Of course, Nigel, you are right. With current balancing resistor I know it's possible to parallel diodes (and transistor). But without resistors, I think it's easy to burn both diodes (or bridges or transistor) one after the other. Am I wrong?

 

[mneary]

Of course, Nigel, you are right. With current balancing resistor I know it's possible to parallel diodes (and transistor). But without resistors, I think it's easy to burn both diodes (or bridges or transistor) one after the other. Am I wrong?

The prohibition is often repeated, but the risk is overstated.

A silicon diode has a negative coefficient of voltage with respect to temperature. In theory one diode which is hotter will steal all the current and keep getting hotter. It will blow, leaving all the current to the other one which will blow next.

This ignores the fact that real diodes aren't perfect, and they have internal resistance. A diode carrying a higher current will usually have a higher voltage drop. Often this is enough to allow equitable sharing. For added safety, you can thermally couple them, and add external resistors.

At the end of the day, circuit which has properly rated parts will be the most reliable.

 

[Nigel Goodwin]

Of course, Nigel, you are right. With current balancing resistor I know it's possible to parallel diodes (and transistor). But without resistors, I think it's easy to burn both diodes (or bridges or transistor) one after the other. Am I wrong?

Yes, you're wrong, as I said, it's common commercial practice to parallel rectifiers.