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220Vac to 5Vdc Transformerless Power Supply Using LNK304


Whenever you hear the transformerless supply term, you initially imagine the capacitor-based solution, which means a high voltage capacitor in series with the mains line, then a bridge rectifier, a Zener diode, a filtering capacitor, and so on. Such a circuit is not just able to deliver sufficient current for many applications, also, it is not a reliable solution for the industry, although you might see such circuits in some cheap products that are designed to have a low cost.

A month ago, I was repairing a washing machine mainboard. In the examination process, I realized that it is equipped with an LNK304 chip that is used in transformerless supplies. So I decided to design a circuit based on this chip to be used in your applications. The circuit contains 220VAC mains input protection, output filtering, and a regulator.

To design the schematic and PCB, I used Altium Designer 22 and the SamacSys component libraries (Altium plugin). To get high-quality fabricated PCB boards, I sent the Gerbers to PCBWay and purchased original components using the To test the current handling and stability of the output voltage, I used the Siglent SDL1020X-E DC Load and examined the power supply output noise using the Siglent SDS2102X Plus oscilloscope.


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