“LNK304 Transformerless Power Supply
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 componentsearchengine.com. 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.
This circuit is for educational purposes only and it is directly connected to the 220V-AC Mains. if you are not familiar with the electrical safety rules, please avoid this content or ask some professionals to help you. The author (or anybody else or any company) is NOT responsible for any harm or damage. Do it at your own risk. This is not for beginners!
- Input Voltage: 220VAC+/-15%
- Output Voltage: 5VDC
- Output Current (Continuous): 120mA to 150mA (can be increased, see text)
- Output Current (Short time): 180mA
- Output Noise (max): 30mVp-p (150mA load, 20MHz BW)
- Input Protection: Fuse, NTC, Varistor
- Output protection: short circuit and current limit at around 190mA”