LED Driver design- DER286

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Dear Sir,

I am from Kolkata, India.
Using PI products regularly.

I have assembled circuit of figure-4 of DER-286. Transformer design is attached.
I have reduced R10 to 54K as to drive 2X(1WX9 nos) LED strings. OP- 27V, 650mA.

But, PF is as poor as 0.65.
Middle portion of input current wave form is having high spikes and not at all matching with the image of DER-286.

PLEASE HELP, so that PF is 0.9 +.

Your prompt reply will be much appreciated.


SN Ghosh

Link-PH-30W-2.pxlph39.2 KB

Hi SN,
There are 2 major reasons why the PF is significantly reduced.
1. DER286 is designed around 30W, thereby reducing the output without updating the EMI section will reduce the power factor. You need to optimize the EMI circuit for lower cost and better PF.
2. LNK419 optimum performance is around 18W to 50W for wide range operation. I think you can use LNK418.