36Watt LED Driver

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 I have designed the LED driver for 48V @750mA, amounting to 36W, using PI expert and fine tuned using PI spreadsheet . The desine is attached for the ref.

Instead of RM12, the circuit was designed for ETD34. Following are the observations and problems I am facing

  1. Layout guidlines were followed as per the PI sample layout
  2. Without LED load, the o/p voltage is about 63v
  3. When connected to the LED, the flickering starts
  4. Removed the Q1, of OVP section
  5. open voltage shots to about 130V
  6. After connecting the LED load, the current was 750mA and voltage was 48V 
  7. But after 10-12 minutes, the o/p diode gets heatsup and whole circuit shuts down
  8. The LNK419 is not so hot, but it is warm

Kindly guide me to resolve the issue

36W_NON_DIMM_48V sch.pdf22.73 KB


1. Check your actual IFB current, flickering may be caused by skipping cycles if IFBskip is exceeded or IFB falls below IFBAR. Make sure operating IFB is within the window of these 2 limits. The OV voltage depends on the zener and coupling between your bias and output winding. Make sure Q1 is not triggered during normal load conditions.

2. If you remove Q1, there is no open load protection thats why output voltage will shootup

3. If output diode heats up, there could be a significant reverse recovery losses on the diode you used. This reverse recovery current might also trigger the peak current limit on the primary side. I suggest you use faster diodes with trr of 25-50ns if you operate mostly in CCM