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5V 10A 50W industrial switching power supply

(Reverse Engineered Schematics)

The schematic of an industrial switching power supply module S-50-5 in a metal housing. It's a flyback topology. The input is 100-120V~ or 200-240V~ selected by a switch, 50/60 Hz. It contains no control chip and no MOSFET, just bipolar NPN transistors. It contains TL431 voltage reference and 4N35 optocoupler. The power switching transistor is 2SC3679 (C3679). It has a proper fuse, NTC thermistor, class X2 and Y1 safety capacitors, snubber networks, EMI filters, overvoltage transient protection varistor (MOV), good isolation distance and a relatively safe-looking transformer. But i didn't examine the safety of the isolation inside the transformer. The only problem of this switching power supply is the way the power transistor and diode are mounted on the heatsink! Just the corners of their packages are pressed onto the heatsink! The power supply is not so bad, but you have to properly mount the power diode and transistor onto the heatsink yourself. You can also ground/earth the negative terminal of the output for more safety.

Switching power supply module 5V 10A 50W type S-50-5.

Disassembled switching power supply module 5V 10A 50W type S-50-5. It was in use, 4 capacitors (all 2200uF 10V) failed. After I replaced them, it works again. I also improved how the power transistor and diode are mounted on the heatsink (the diode mount is removed in the picture).

The label of the S-50-5 power supply module.

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