LNK306 is getting damaged

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Hi PI team
Please find the attached schematic.We are facing following problem
1) Fuse is getting blown
2) LNK306 is getting damaged
3) Output voltage are same as Input voltage

Please let me know following
1) Does connection of phase and neutral will make any difference ?
2)What is could be possible reason for fuse getting blown?
3) What could be reasons for LNK306 getting damaged ? Does LNK 306 will cause some instantaneous inrush current ?
4) what could be reason for output voltage getting same as input voltages?

첨부 파일Size
SCH_501-1-01039_A1.pdf26.56 KB

Hi abhishekoct18,

Please help answer a few questions below to help better understand the nature of the problem:
1. Does the IC failure occur on startup only or while it has run for some time?
2. Does the IC failure occur when the relay circuit is not connected (or when it is reset)?
3. Can you give the output loading specs of your circuit?

Thanks.

Hi Jango
Please find below answer
1)IC failure is happening only at startup . Till now i can't able to run any device successfully .
2) IC failure is happenning at startup only when relay is not connected.
3) Max load current is 40 mA @12 V.

Just to clarify, IC failure does *not* happen when relay is connected? This might suggest your circuit needs a pre-load resistor. Try adding 10k resistor at the output and check if output voltage regulates at 12V, without the relay disconnected.

Hi Jango
By default relay is not enabled, it will be enabled only after say 220Vac (configurable). We observed failure at 100 Vac also, as wll as 220 Vac. So beleive it is independent of relay.

As per application note 37 optocoupler feedback network don't need pre- load resistor,what makes you feel that we need pre load resistor ? Basically i need to understand why pre load resistor is required even in other feedback network.

Hi abhishekoct18,
You are right, the zener will clamp the output voltage if needed at no load. But to be sure, I suggest that you probe the output voltage at startup. You said that the failures occurred after the output capacitor capacitance and voltage rating were changed, so the failure might be related to output voltage.