Clamp circuit ?

Posted by: Astrid on 05/07/2014

I have a few questions about the clamp circuit for TOP Switch.

Example PI Expert suggest

RCD+Zener Clamp

RC=3x 33k, CC=8,2nF+TVS Zenern180V

Estimated Clamping Voltage =177V VDRAIN=608V

if I change RC on 3x22k and CC=10nF

the Estimated Clamping Voltage =142V VDRAIN=570V

What will be the impact on the efficacy and why the first solution is better than another?

Comments

The efficiency is always affected by the RCD snubber. The efficiency of the second solution should be lower since the voltage stress on the TOPSWITCH is lower than the first solution.

If you care about the power loss at no load and light load, the RCDZ snubber is a lot better than RCD snubber, because the zenner limits the snubber loss significantly at ligh load/no load. If no load loss is not a big issue for you, RCD snubber is a good choice becasue of lower cost.

Regards

Thanks for the info.

Voltage rating of the MOSFET is 725 V, I take it that you consider to 625V for reasonable and safe maximum in real construction?

Actually the design has to meet the derating requirment from the customer, and different customers have different derating requirements. For me I think 625v is reasonablebecause of the 86% derating.

But again, customer requirment is the key, and you may have to contact with your customer first.

Regards