How to Determine AC and DC Pins for a Full-Wave Bridge Rectifier?

[kasraian]

1. Quick question about Full-Wave BRs. If you have a FWBR with unmarked pins, how do you figure out the AC pins and the output DC pins?

 

[Zryn]

Do you have two diodes, four diodes or a black box?

See Wikipedia's simple circuit diagram below if you can see all four diodes (with cathode strip).

 

[kasraian]

4 diodes. I was just thinking about measuring the full-wave bridge rectifier pin to pin using a DMM in diode mode. Then drawing the schematic and concluding the inputs/outputs from their. Is that a good idea?

 

[Zryn]

If you can see the 4 diodes, you should notice a silver strip on one side indicating the cathode (negative), and then you can compare their orientation to that picture.

If you can't see this strip, then yes, doing a diode test will tell you. You should either get the voltage drop for the diode (0.6V to 0.7V) when you have the positive lead on the anode (positive) and the negative lead on the cathode (negative), or something like OL (overload) showing a bad result.

 

[vk6kro]

4 diodes. I was just thinking about measuring the full-wave bridge rectifier pin to pin using a DMM in diode mode. Then drawing the schematic and concluding the inputs/outputs from their. Is that a good idea?

Yes, that is an ideal way to do it.

Also, you will often notice that bridge rectifiers have a sinewave symbol on the input pins, and a + sign and a - sign on the output pins. The sinewave refers to the AC input.

If only the + and - signs are present, the other two pins are the input.