4 or 2 diodes

[electrolitic]

It is an old question, still unclear: Why some designers apply 4 blocking diodes, instead of 2, when connecting two DC power sources in parallel. There is a risk of, under certain circumstances, the output voltage be the sum of the two sources. Is there a reason that justifies this risk?

 

[LionelHutz]

Do you mean only diodes on the positive vs diodes on both the positive and negative? If yes, the 4 diode cas is likely to prevent the negatives from backfeeding into each other. The reason for wanting to prevent that might depend on the power supply design.

 

[electrolitic]

Diodes on both the negative and positive. Thanks LionelHutz but if you have an electrical connection between the positive output of power supply #1 and the negative output of power supply #2 (both grounded, as an example-it is not a short circuit because some diodes are blocked) you will double the output voltage. It is a very serious failure, worst than negative backfeeding,I guess.

 

[petronila]

Hi Electrolitic

Both are full wave rectifiers. Two diodes type is used when with center tapped transformer. 4 diode rectifiers no need a center tapped transformer. This type is called bridge rectifier because rectifiers are mounted in the form of a Wheatstone bride. Mainly difference is the Peak inverse voltage of diodes (in two diodes rectifiers is twice).

Regards

Petronila

 

[LionelHutz]

Sure that is a failure which could happen. But, the decisions to use 4 diodes are still dependent on the overall design.

 

[itsmoked]

Annoyingly, you lose your ground reference with a bridge rectumfryer.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electrolitic]

itsmoked
It is not a question of ground reference. It is simply a way that makes a connection between two points and simply doubles the rated output voltage. To lose all the connected instrumentation it is not a simple failure.