Rectifier Return Current and GND Question

Thread Starter


Joined Aug 7, 2020
Hi all, I am still a beginner and I have a question about the return current path of the rectifier load during unexpected event, such as arc.
Please see the attached image for the example of the circuit.

This is a circuit of a power supply unit powered from mains. It will eventually have a box which enclosed the circuit, made up of metal and connected to earth ground pin. Now here's my question:

1. I know that all rectifier load current will always return to -ve terminal. But what if something bad had happened and a arc occur at the transformer side. Since there is two possible return here, one is the common on the rectifier and another the GND-connected metal shield. Lets say they are both close enough to arc over, will the current always return to the source, in this case the rectifier, or the current will go the metal shield which is lower potential. or both?

2. Secondly, let's say when the tranny is off and the transformer inductances causes a voltage spike at source side of the tranny and the diode for some reason was broken. If the voltage spike is high enough, will it arc over to the metal case, or would it arc over to the rectifier common GND? or both?



Joined Jan 29, 2010
hi d1,
Welcome to AAC.
As a 'beginner' it is recommended that you do not attempt a build of a mains powered supply that is not isolated, as you should be aware, this type of power supply can give a lethal shock.


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Thread Starter


Joined Aug 7, 2020
Hi moderator, I am not really building a power supply. I am troubleshooting one that blew up and I tried to find out why it happen. And while troubleshooting I came up with hypothesis of my own, but a few points that I have made seem to challenge my knowledge about electronics. Then it occur to me that my knowledge is not perfect and I needed guidance.


Joined Apr 26, 2005
Which diodes did you find defective?

For instance, I've found in numerous cases post heavy thunder storms, the two diodes connected to the AC return side open. This was because of lightning current being introduced into the ground .... which is tied to the AC return at your distribution box. After all, the median lightning stroke is 50,000 amperes with a duration of about 5 microseconds.