I built and have been using this power supply for sometime…until yesterday when it blew 2 diodes. I managed to find the bad componenets and fix the power supply but then the questions about what happened came to mind…
It appeared that the potential on the middle (ground) pin was above earth ground. Measuring between the earth ground and the middle pin (after it was fixed) shows a voltage potential of 36v!!!
No wonder the spark was so big!
It works fine, powers my other projects fine… Should there be a voltage potential between the middle (ground) pin and earth ground?
The unit uses a three wire cord and the case (metal) is at earth ground.
I am not talking about the two chips. In the diagram of the circuit and the board layout the connector labeled SK3 has three pins; +, 0, -. If I take the middle pin to earth ground (the metal case of the power supply) there is a 36v potential.
This potential carries into the ground of any circuit I power. When I hooked up an oscilloscope ground (earth ground) to the ground of the circuit that was being powered, it drew a large spark and fried the power supply. Fortunately it does not seem to have hurt the oscilloscope.
My question is: should the pin labeled 0 on SK3 have a potential of 36v to earth ground?
No it should not, but this has nothing to do with the kit.
Due to a wiring or mechanical error either the + or the - is touching the metal case, e.g. at the heatsink.
It was the heat sink touching the case…thank you very much!
I like the power supply; put it in an old computer power supply box and it is rugged. The heat sink was added as an after thought. Not thought thru well enough.
This is a symmetric power supply.
It outputs a positive voltage and a negative voltage.
They are mostly used for amplifiers that use a push pull setup.