LNK304 blows at power up
I am using a LNK304 for a 90-277VAC to 5V, 20mA converter. When powering up at higher voltages, the LNK304 blows. I need the design to be small, low cost, and all surface mount. The schematic is attached. The capacitors are all ceramics. The inductor is a Bourns SDR0403-681KL. A fuse is used because I could not find a surface mount fusible resistor rated for the voltage.
Comments
The board runs fine at lower voltages or when the voltage is ramped up through a Variac so the diodes seem to be fine. Does the LNK304 have stability problems when the impedance of the output capacitor is too low? I was more concerned with the ceramics on the input side with surge through the current limiting resistor but didn't know how this would make the LNK304 blow up.
it use non linear control, so you never worry about the loop problem.
PLS check the drain pin voltage and current, and ensure low voltage stress on part and no current spike/ saturation issue.
The input voltage and inductor look fine. I have tried various things but it keeps coming back to the ceramic input caps. If I use an electrolytic cap of similar capacitance, I don't have a problem. If I use a ceramic cap, it blows at high voltage. Usually, the ceramic cap is fine, only the lnk304 is damaged. I have tried various PI filters to reduce the surge but without success.
The ceramic capacitance is reduced significantly with DC bias. You may have to use several ceramic caps in parallel to make sure the capacitance is high enough at high line and also to take care of the thermal problem of the ceramic cap. LNK switch used a lot, so I believe the part has no problem at all.
again, thanks for using PI part.
Thanks a lot for using PI parts!
The schematic looks good. But PLS confirm the polarity of D2 and D3, and check resistance between output and output return. Ceramic cap can results in short circuit problem at output.
good luck!