TOP271KG IC burnt

Hi Hock,

Thank you very much for using Power Integration's TOP271KG. We understand that there was a failure however could you also tell us what condition is it failing? The schematic looks ok but we would like to understand the nature of the failure so that we can pin point exactly if this is a design or component problem. Have you checked the drain voltage before the failure? Thanks.

I have upload a photo showing the tracks that connected to Pin 1 and after D105 was completely burnt. This incident happend in China where we suspect may be due to unstable voltage supply. I raised the input voltage to 260V AC and found out the Vds is 718V, very close to the MOSFET rating of 725V. I am thinking of changing the values of the RCZD clamp to lower the Vds, may I know the formula to do the calculation and decide the value? The zener diode in the RCZD clamp is 200V, do I need to increase the value?

Thanks

Hockleong

Hi Hockleong,

We suppose you are already close to the breakdown voltage. Is the 718V measured voltage the peak one? By the way what is the ratings of your snubber circuit? Let us check and verify it. There's a big possibility that this is where the failure is coming. Probably it's the snubber circuit. 

Hi,

Yes 716V peak voltage refer to the photo attached(reading in the red box). The clamp resistor is 56k 2W, and capacitor is 2n2 630V, zener diode is 200V 600W, snubber diode is 600V 1A.

If I would like to reduce the peak voltage ripple, can I change the R 56k to a lower value, I know it will lower the peak but trade off with higher losses.

thanks for you help.

HockLeong

Hi Hockleong,

Yes you can change the value of the resistor or even the capacitor to lower down the peak voltage. If you have still some margin on the efficiency then it will not hurt much to adjust the snubber valuues. Otherwise you can check on the transformer contruction and lower your leakage inductance.