LNK410 by PI Expert Blocking Diode Unnecesary?

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Hi everybody,

I allready desing a driver with LNK410, using PI Expert, I did it with all compenents described, and then, I had output only 5v, I check double twice, I did not find nothing wrong, I take out all diodes to check them and I forgot to solder a blocking diode (fr257), the driver stars prety nice, led string of 75w get full light, but now I can not dimmer without flashing and buzz noise.

question, what is happen? if I put the fr257 this make output drops, and star uneven reading at all.

in ther way I take out the fr257 and star ok, but with out dimmeraizing.

can you help me to fix it? , schematic included

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LNK410 by PI Expert19.84 KB


The diode is used for clamping the drain voltage and make sure that it does not exceed the breakdown voltage (725V). It is therefore necessary. Please check your connection or optimize the clamp circuit. I attached a sample DER that used a diode-TVS clamp. You can try that instead.

di278.gif13.92 KB

Hi, thanks for answer

While read you comment I make a fixture to test the FR257, I check 20 of them all fail, Now I know, I have a bad lot of diodes, instead of this diode a put a IN4937 and is working, but, in no load, output goes high 65v  coul it damage output filters?

If the output capacitor is underrated then it could damage it. Either use an 80V-rated cap or optimize the ovp circuit (add the circuit if you don't have).


Well, yes the capacitor is underrated, but, I am working to reduce size of the driver and i got no space for bigger capacitor, so I am going to add the circuit and use a SMD devices, I will you comment.

thks a lot