DER337_LNK460_VR1 (SMAJ350A) break down and shot circuit

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Now, we make LED Driver follow PI (DER337_LNK460) sample 100 pcs and install at office in Thailand. We have problem about VR1 (SMAJ350A) break down and shot circuit 3 pcs.We should be changed range part VR1 (SMAJ350A) to SMAJ400A. Please suggest about rout cause problem VR1 (SMAJ350A) break down and shot circuit . 

Did the failure occur immediately after powering up the LED driver? What is the AC mains voltage?

By changing VR1 to SMAJ400A, you are suggesting that the problem is due to voltage stress. At 230V input (325Vpeak), the diode is not even conducting. At 265V, there is a small portion in the AC cycle that some leakage current will flow. However, the diode is meant to clamp at even higher voltage (390V to 430) and unless there is reliability problem on the part itself, it could be something else.

 

If the failure happens immediately, please verify if the diode is mounted with proper orientation or there will definitely be short-circuit due to diode failure.

 

Hi. I have same problem with all 3pcs samples I made with same der337. Problem was in China with AC233. It seems manufacturer of SMAJ350A can be different. I didn't try with right one as on datasheet yet. So on mass production, can I just not assemble of VR1 as we have RV1 for 430V protection?

Please do an actual surge test based on your requirements and this will tell you if you need to put the TVS diode or not.

DER-337 was verified at 1kV differential surge, so if you only need to pass 500V, it is possible to remove the diode, but you still need to verify it by doing the actual surge test verification.