LNK304 Transformerless Power Supply

[Hesambook]

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.

References
main: https://bit.ly/3KoNPXJ

DB107G schematic symbol, PCB footprint, 3D model: https://componentsearchengine.com/part-view/DB107-G/Comchip%20Technology

LNK304G schematic symbol, PCB footprint, 3D model: https://componentsearchengine.com/part-view/LNK304GN-TL/Power Integrations

78M05 schematic symbol, PCB footprint, 3D model: https://componentsearchengine.com/part-view/MC78M05CDTG/onsemi

Electronic designing CAD software plugins: https://www.samacsys.com/library-loader-help

Altium Designer plugin: https://www.samacsys.com/altium-designer-library-instructions

Siglent SDL1020X-E DC load: https://siglentna.com/dc-electronic-load/sdl1000x/

Siglent SDS2102X Plus oscilloscope: https://www.siglenteu.com/digital-oscilloscopes/sds2000xp/

 

[Easy peasy]

beware breakdown of the buck choke in these circuits - they are usually built to a price and not made to withstand the high volts ( >= 325 Vpk ) that they are hit with - a eventually cause the controller to die ...