220V-AC to 12V-DC 18W Switching Power Supply

[Hesambook]

Flyback is the most common circuit topology to build galvanically isolated AC to DC or DC to DC converters. Flyback circuit is cheap and relatively easy to manufacture, therefore nowadays the majority of home or industrial appliances are powered using AC to DC Flyback converters. In general, a Flyback converter is suitable for low-power applications, mostly below 100W.

In this article/video, I designed a cheap AC-to-DC flyback converter using a DK124 IC that can deliver up to 18W continuously. I calculated the transformer to handle 12V at the output which can be easily modified to reach other output voltages as well. The DK124 chip does not need any auxiliary winding or even an external startup resistor. The 220V Mains input has been protected using a MOV, an NTC, and a Fuse. The PCB board is single-layer and all components are through-hole.

To design the schematic and PCB, I used Altium Designer 22. The fast component search engine (octopart) allowed me to quickly consider components’ information and also generate the BOM. To get high-quality fabricated boards, I sent the Gerber files to PCBWay. To test the power supply, I used Siglent an SDL1020X-E DC Load, an SDM3045X Multimeter, and an SDS1104X-E/SDS2102X Plus oscilloscope.


Specifications

Input Voltage Range: 85 to 265V-AC

Output Power: 18W Continuous

Output Voltage: 12V-DC

Switching Frequency: 65KHz

References
Article: https://bit.ly/3Be4Jqd
[1]: DK124: https://grupoautcomp.com.br/wp-content/uploads/2016/11/Specification-IC-DK124.pdf
[2]: 10D561: https://octopart.com/mov-10d561k-bourns-19184788?r=sp
[3]: PC817: https://octopart.com/pc817x1j000f-sharp-39642331?r=sp
[4]: TL431: https://octopart.com/tl431aclpr-texas+instruments-521800?r=sp

 

[InsAndOuts]

Nice work!
Just curious, as I don't look at SMPSs that much. What range of efficiency and standby power did you reach?
I also wonder how you decided about the cutouts for the creepage.
The fuse seems a bit close to the DK124 but the creepage is still OK?

 

[Hesambook]

Nice work!
Just curious, as I don't look at SMPSs that much. What range of efficiency and standby power did you reach?
I also wonder how you decided about the cutouts for the creepage.
The fuse seems a bit close to the DK124 but the creepage is still OK?

Thanks, I have not measured the efficiency and standby current independently, but when we use an embedded chip like this (not discrete components), we can rely on the ratings of the chip

Creepage is necessary when we deal with HV, especially when one line is HV and another one is GND or far lower. distance between the fuse and the chip is quite high. There is a standard for this, I don't remember the code. just search about track clearance and creepage

 

[InsAndOuts]

Thanks.
Well I don't see ratings on smps level efficiency and standby usage in the DK124 datasheet. I may be looking at the wrong place. Now I notice the fuse holder has a good enclosure, no problem with creepage indeed.

 

[Calm down]

Hello brother, with all due respect, you can have a better choice. For example, PL3328BD, CR6249TM, etc. can be used to construct a 24W power supply without the need for optocouplers and 431.

 

[Hesambook]

Hello brother, with all due respect, you can have a better choice. For example, PL3328BD, CR6249TM, etc. can be used to construct a 24W power supply without the need for optocouplers and 431.

to offer tight regulation, such a feedback path is mandatory. otherwise there are some chips that work without feedback components and regulate based on primary current or an auxiliary winding

 

[maxymum]

Hey Bro, and thank you in advanced for redesigning dk124 circuit to a better version.
I have a problem with your circuit. i made it from the scratch and with your design guide from this link https://www.pcbway.com/blog/technology/220V_AC_to_12V_DC_18W_Switching_Power_Supply_81665a6c.html
the problem is that when i dettach the transformer there will be around 300 v on trans input and it seems that dk124 is working properly but when i connect the transformer there will be no output on transouput. i think there may be problem with my transformer winding or something like that. can you explain more percisely that how is the winding procedure? i ordered 4 transformers with different winding directions and non of them are working. I'm living in Iran and any help from you would be apreciated.

 

[Calm down]

On the high-voltage side of the transformer, the incoming line is connected to DK124 (5-8), and the outgoing line is connected to the positive pole of the high-voltage DC bus. The low-voltage side of the transformer is connected to the rectifier diode, and the outgoing line is connected to the low-voltage side ground wire. Do not reverse the direction of the transformer during winding, for example, the high-voltage side should be from left to right, and the low-voltage side should also be from left to right. Due to the flyback scheme, the transformer belongs to an energy storage device, so it is necessary to polish the air gap in the magnetic core column to ensure that the inductance of the high-voltage side winding of the transformer is within the required range.