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I built this power supply from used parts pulled from Asus LCD monitors. I used the service manual and FSDM0565R datasheet for reference.

Parameters:

• input: line voltage 230 V
• outputs: 12 V / 0.4 A and 5 V / 2.9 A

The transformer is of type SPI 8TT00048 and there is no data on it, as usual. Pins are tied to doubles on the secondary, GND is in the middle.

The main winding that is used for reference, is 12 V and the supply works correctly only if this rail is loaded.

My measurements when only one rail was loaded:

• 12 V rail: 11.4 V 0 A, 10.7 V 0.1 A, 10.3 V 0.2 A, 10.1 V 0.3 A, 9.8 V 0.4 A
• 5 V rail: 5 V 0 A, 4.9 V 1 A up to 1.2 A, then it turns off

When I loaded the 12 V rail with a 68 ohm power resistor, it supplied 150 mA without 5 V rail loaded, however, the current increased to 190 mA when taking maximum current (2.9 A) from the 5 V rail.

• 5 V rail with 68 ohm resistor on the 12 V rail: 5 V 0 A, 4.9 V 1 A, 4.8 V 2 A, 4.7 V 2.9 A, turns off around 3 A

So the end result is that for some reasonable current from the 5 V rail, the 12 V rail must be loaded.

The schematic

Click to enlarge.

PCB

Dimensions: 15 x 10 cm. Bottom traces are turqoise, top traces are black. The red SMD parts are soldered from below.

Click to enlarge.

Conclusion

I played with this circuit because I had many parts from dismantled SMPS power supplied and I succeeded in building one.

However, I don't like the noise of this supply with pitch depending on current taken. When at least 2.3 A is taken from the 5 V rail, noise stops and when current lowers again, noise returns. So, this circuit will only be useful for something that takes at least 2.3 A from the 5 V rail and is able to load the 12 V rail with at least 150 mA (or have a really hot power resistor). With zero load the supply is silent - the IC switches to standby mode. Originally, I had built this circuit on a veroboard, but it was not working optimally and I hoped that with a proper PCB the noise will not be present, but it persisted. A pity...