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Freewheeling diode breakdown using LNK304DN

Posted by: AndrisIgaunis on Thu, 06/02/2016

Dear Sir or Madam, 

In our design of Buck converter from 230 V AC to 6.3V DC using LNK304DN, we are experiencing rather frequent cases of freewheeling diode D1 breakdown. We are using diode ES1JL from Taiwan Semiconductor. The output current is up to 100 mA. Can you give any comment on whether the diode is selected properly, or there is another mistake in the design? 

The load includes a relay coil switching (inductive load), but it is switched rarely and portected by separate Zener diode. 

Yours faithfully, 

Andris Igaunis


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Submitted by PI-NANO on Fri, 06/17/2016


I saw that the inductor L3 used in the design was under rated and as a result it is getting saturated. The inductor saturation current rating should be atleat 30% higher than the device maximum current limit. Datasheest max. current limit for the LNK304 is 345mA, I would suggest you to select the inductor current rating about 450mA.

I have also observed that you are using 10K for R11, however the recommended value for R11 is about 2K, based on that you will have to readjust the value of R10 as well to get required output voltage.

I would suggest you to go through the following app note. Read Select the Feedback Resistors section in page 10.