12V 5A 60W switching power supply (LH-1205)
(Reverse Engineered Schematics)
Schematic of the LH-1205 12V 5A 60W switching power supply from China for $3. The insulation distance on the board looks very good. The suppression capacitors are proper safety classes X2 and Y1. There is a fuse (T 3.15A) and interference filters. There's also a nice snubber network on the primary winding of the transformer. Regulation is with EL 817 opto-coupler and TL 431 voltage reference. The control chip is in a 6 pin SMD package, marked "49 309". Most likely it is XN1049. However, there is no inrush resistor or NTC thermistor, the inrush current is limited only by the resistance of the EMI filter winding. The switching transistor HFS740 (similar to IRF740) is a MOSFET, rated only for 400V, which is quite low. Typically, 500 or 600V types are used in this location. The secondary rectifier Schottky diode 20L60CTF is only rated 60V, I would expect something like 100V. The label says the maximum output current is 5A, but the overload protection switches off at 3.6A. On the board there are remains of original cables that were cut. New cables were soldered to it (very poorly). The SMPS was apparently repurposed. The new output cable is soldered to the 1000uF 16V capacitor, bypassing the EMI filter! The worker who "recycled" the board probably did not know what he was doing. He just soldered the cable to the largest capacitor he saw on the secondary side. The LED is also added and its series resistor is freely in the air.
Chinese 12V 5A 60W Switching power supply
The label says AC/DC Adapter Model LH-1205. 12V 5A 60W. The input is 100-240V 50-60Hz.
The SMPS without top cover.
The PCB board of the 12V 5A 60W power supply from THT (through hole) compoment side.
The PCB board of the 12V 5A 60W power supply from tracks and SMD (surface mount) compoment side.
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