DER-479 modified schematic issues
We are using DER-479 as reference design for our 400V AC power supply (5V, 0.3A output) and have some issues with transformer design / feedback.
I've attached current schematic with transformer specification we received from our subcontractor.
One of issues we noticed early is that input is connected to primary turn split instead of full primary windings. But even with this issue corrected,
there are still issues with LNK4004D periodically going into sleep or restarting at 40mA or 80mA loads.
Can you specify relevant test points for our schematic so we could look into it at better detail?
According to PIXI, we should try 150T/150T primary, 16T secondary and 21T feedback based on our entered specs.
Can you recommend transformer design for our application?
Comments
Thanks for information, we will try suggested transformer.
With current supply design we are fixed with EF20 and LNK4004D.
For new design we will use lower wattage ICs (LNK6406 or similar) with smaller core.
Attached results from PIXI
| Attachment | Size |
|---|---|
| lnk4004_trafo_test_param.png (504.51 KB) | 504.51 KB |
Hi DariusP,
Thank you for providing us the spreadsheet. Based from this, your design might also work. But your inductance is much higher than the other design we provided you. You can try to test both of the design and check which can provide a better performance.
Best Regards,
PI-SevenofNine
Hi DariusP,
Good day! Thank you for using PI product on your design. Do you have the raw file or screenshot of the PIXL you made? This can help us check your design.
But regarding your testing, you mentioned that initially the transformer primary was connected to the split rather than the full windings, making it 180T primary, 11T secondary, 21T feedback. The primary inductance for this case I believed is divided by 2 from the figure you sent to us, which means around 3.4mH. With that very small inductance you are increasing the peak current which might be very close to the peak current limit (VCS_MIN).
Then you tried to correct it by connecting the primary to the full winding giving you 180T/180T primary, 11T secondary, 21T feedback. With this design the reflected voltage is very high at 165V (VOR = 5*360T/11T). With the given inductance (6.8mH) and VOR, this can also trigger the peak current limit (VCS_MIN).
According to your drawing, you also have a 5V post regulator. It is better to design the input to this regulator by 0.5V to 1V greater than the output. With EF20 core, you can try this transformer design, 62T / 62T primary, 8T secondary, 14T feedback, inductance value = 10mH. Components value as R23 = 270 ohm, R18 = 2.7 ohm, R20 = 16.2 kohm, R21 = 4.87 kohm, C13 = 2.2uF.
Another thing, are you fixed with EF20 core? and LNK4004? Because you are only dealing with smaller wattage. Maybe you can consider smaller core size, IC variant such as LNK4002 or LNK4003. Thank you.
Best Regards,
PI-SevenOfNine.