LNK3694G SMD-8C failure

Posted by: Mayurkatkar on 02/10/2026

Hello team,

We have designed 3W flyback converter for universal input.

No auxiliary winding.
Opto based secondary feedback.

We have got failure as below in only one device. Other all devices working fine.

LNK3694 drain to source pin shorted. LNK3694 switch is burned.
optocoupler collector to emitter pin shorted. Opto is burned. Opto diode is ok.
After bridge rectifier and before input DC link inductor is placed. This inductor is burned.

Note: After replacing all three components, power supply is working fine.

What may be possible reasons for this failure?

Can you give some suggestion so that we can recreate this failure?

Comments

Hello Mayurkatkar,

Good day and I hope you're doing well. Below are some possible reasons that causes of the failure.

It is possible that one of the three components mentioned is already damaged even before powering up the power supply.
It is also possible that the drain pin and source pin of the IC were shorted through solder or maybe an unwanted conductive material that made them short (this also applies to the primary pins of the transformer), causing the IC to be burned.
Also, the optocoupler might be soldered in the wrong orientation.
Another possible reason is that there may be an unwanted power surge during the time that you're testing the board.

Please also double-check that the components soldered on the board are correct and before powering up the board, I advise cleaning it first using a small brush to remove any unwanted conductive material.

I hope that the above information helps. Let me know if there's anything else that I can help you with.

Thank you and I wish you a great day ahead!

Best regards,

Tommy