Help me fix Led Driver 4-8W(LNK403), 36W-39W(LNK420)

3 posts / 0 new

Dear PI.I send to you Schematic design and excel file design for LED driver 4-8W, 36W -39Wwith 2 design i have problem i dont understand.
With leddriver 4-8W: i'm not keep voltage/ current stable, in design i set 4-8W. But when testing it, i only control 2W but not stable.With led driver 36W - 39W: the transfomer of led driver is not noise (have sound, i have try change value block snubber but not ok). and current not stable.
i hope you help me solution for fix led driver
Thank

Hi,

For 36W; 56V/700mA:

Normally the transformer will not create unwanted sound unless the driver is not stable:

 1. C13 should be close to the IC as possible.   Try putting 100nF directly to IC pin to improve the present layout.

2. U1 postion on the layout is not optimize.  Move U1 on the other side of the board to shorten the length of drain path and isolate the drain signal to EMI filter.  In this approach noise due to the switching will be minimized so as the radiated noise.

3. Flip the orientation of D1 once U1 is moved to the other side of the board. This will create a ground barrier between your EMI filter and DCDC.  You might be able to remove and save one EMI choke.

4. I like your loop on the output.  Improve your loop on your auxilliary.  Target to have a small loop as possible for R18,D6 and C11.

5. Varnish the transformer to remove interwinding noise. glue core to the bobbin to remove vibration.

6. Your inductance is too low.  Please refer to the attached spreadsheet for reference.  You can even use RM 10 for cost reduction and for more PCB space.

For 4-8W design:

 You can adjust RFB (R15) to increase the output power. At the beginning you do not need R17.  Put it when you are in the stage of improving theline regulation. 

 Note that this is a single stage PF corrected converter, threfore high output current ripple can be observed (double the line input frequency). I hope the instability you are seing is not related to this parameter.

By the way, make sure you are using the actual LED.  Do not use electronc load that is not intended for LED application.

Regards,

PI

  

i very hope your help.

i fix design and do steps you give me.

Thank you very much.