LNK306 random diodes failures

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Hi All

Attached is the circuit I am using to power my SMPS, at random power-up D5 fails (short circuit).

I noticed that the first time when the circuit is connected to a variac (PFC not operating) it was working fine, I tried to change the AC-INPUT voltage going from 100VAC to 240VAC then it stopeed working while I was playing with the voltage.

Today, at 175VAC I powered it up then the same story, D5 shorts out.

Any idea on why I am facing this issue? is it because of the diode type?

I am using 600uH inductor not 1MH because noise is LESS at that value


LNK306.pdf49.13 KB

I knew that I will never get help here, moving to the VIPER family, best products

Hi MicroSim,

This design should be OK. I can't see any reason why D5 should fail in your circuit. We are recommending a slower diode for D5 but it should not be the reason why it should fail short. Have you tried placing an input filter capacitor? The input DC voltage may not be as stable as it seems.
If this is a new design, please also check pin-to-pin compatible LNK3206 (from LNK-TN2 series) which is an upgrade for LNK306. Design guidelines and examples are also available online.
With regards to the VIPER series, I believe the Power Integrations solution is still the more cost-effective design overall.


I am using MURS160 for both diodes and its working fine until now.

The chip is being fed by a regulated 385VDC from a PFC