Flyback DC-DC converter design

You need to check your transformer design using PI expert PIXLs.

Download the program from PI website and create a new file in PIXLS for the DPA425.

Once you have the file, Enter your input variables.

Then enter your number of secondary turns and change the reflected voltage to match your actual primary number of turns.
Adjust VB to match your bias winding number of turns
Adjust KI to match your actual external current limit

Adjust KRP/KDP to match your transformer primary inductance.

This process is called reverse engineering and needs to be done to check the basic transformer's parameters. Any mismatch of your actual transformer will be showed in the program.

If you can not find the possible mismatch issue, then you may post your schematic, your transformer design and a waveform of the DRAIN current and DRAIN voltage when the supply is not properly working

Hi,

Thanks a lot for the comments.

I have checked the transformer design per your instruction and didn't see issue there.

Schematic and a few waveforms are attached here for further comments.

Transformer design docs are attached as well. More transformer data are as below.

Primary - 18T pins 1-2
2L #1350 tape
Sec - 24T pins 9-7
2L #1350 tape
Aux 14T pins 4-5
2L #1350 tape

The core area for the EP13 core is 0.2cm^2.

Thanks
Henry

I saw your documents. I have not checked your transformer design yet. Can I ask you to disconnect R159 and R20 and connect the L pin of the controller to primary return?

Then run the test again and tell me if the supply works fine at higher input voltage.
PI-Worf

Hi, Worf,

I removed R159 and R200, and connect U59 pin2(L) to pin8(S). The failure is still there.

I noticed drain current already exceeds protection limit(3.5A). So I short R250, the current limit changes to 5A. Then I captured transformer pin1 V/I waveform as attached. The power supply still doesn't work. It looks reflected output voltage is not big enough.

I still need your help on this issue.

Thanks
Henry

Hi, Worf,

Are you still work on this issue?

Henry

Hi Henry,
About two days ago, I sent you a private message to your email. I need you reply for me to send you a transformer design.

Hi, Victor,

I have responded email to you. Could you please send over spreadsheet file?

Thanks
Henry