Issues with LNK409 efficiency

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Hello.

There is an issue with power supply efficiency (counted value is 88%, real value is near 80%)

This is non-diming scheme, with LNK 409 in spite of LNK419, with R6=49,9k. D5 is replaced on 1N5408, VR1 is 1.5KE200A.
Scheme works correctly and stable, but the transformer heats to 75-80 Celsius degrees, the other elements don't heat significantly.

Please advise possible ways of efficiency improvement.

Scheme file is attached.

Measured Values:
In : 235V 0,166А PF0.97
Out: 74,3V 0,42А

transformer: L=1512 uH, Lleakage= 35.8uH

 

 Thanks & Regards.

첨부 파일Size
73.2V_420mA -200V.uds303 KB

Hi,

Efficiency can be easily met with a buck topology.  But then if you are going to stick with a flyback converter the following items will help you to increase its efficiency:

1. Add tape between layers in tharansformer winding.  This will minimize the interwinding capacitance.

2. Replace D10 to a better diode.  Try STTH1R06RL or try a 2A diode.

3. Add heatrsink for U1.  Lower temperature lower Rds(on).

4. Increase Core Size of your TRF

5. Check if there is a room for increasing wire size for TRF.

5. Minimize the drop on your EMI filter.

6. Measure the efficiency using a power meter in the input and output.  Do not use ordinary multimeter because unique input and output waveforms are not intended for these types of instruments.

Refer attached for design example. 

http://www.powerint.com/sites/default/files/PDFFiles/der286.pdf

Regards,

PI-Jono