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12V-7A AC to DC Switching Power Supply [SMPS]


The maximum power delivery of this power supply is 84W, which means it can handle 7A continuously at 12V output. The transformer can deliver higher currents, however, the educational purpose (hand winding of the transformer) and thermal stress on the switching controller were considered (the peak current of the controller’s MOSFET is around 2.3A, at 7A). The controller chip is KA1M0565, which operates using a 470K startup resistor and a small auxiliary winding on the transformer. The transformer's ferrite core is ER28-17-11, and the switching frequency is 67KHz. A potentiometer allows the user to adjust the output voltage precisely and set it to 12V.

To design the schematic and PCB, I used Altium Designer 24 and the Octopart website to quickly gather the necessary component information and generate the BOM. I used the Siglent SDL1020X-E DC Load and Siglent SDS2102X Plus oscilloscope to test the board for voltage drop, current delivery, and output noise. At the maximum output current, the output voltage drop is around 40mV only.


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