200V Zener IN5388B gets heated.

Thread Starter


Joined Dec 4, 2019
Hi, We have standard product which operates on SMPS based power supply, Input 85 - 265 VAC. SMPS designed with TOP 224 Switch. Its a standard design and we din't had any issue since long time, but now we have observed that Zener connected as Clamping circuit of 200V at primary of transformer gets heated and blows after some time. But if we replace it with other fresh zener of same part number and make (On semi) it works. We have gone through the date code also, zener failing belongs to different date code say (1903 or 1805). I have checked voltage across zener it indicates 135V approx. I have contacted to manufacturer (On semi)also, as per them they need to check after receiving item at their end. This will take time, so i need to know that anything else i should check at my end. Is this an issue of transformer or anything else, please help me to check and find reason of failure.