TOPswitch flyback with "active" clamp is OK?

Do you have a PI Expert design file I could take a look at?

-The Traveler

PI expert max power was 244W and it gave me RCDZ snubber and warned me dissipation in the TVS was too much....so i came up with the above "RCDQ" clamp

treez -


I'm afraid I don't have any experience in active clamp design so I can't really comment on how well it will/won't work in your application.


However, a couple things come to mind when you mention excessive clamp dissipation. Proper transformer design to minimize your leakage inductance is going to be especially important. At your power levels, you want as much power as possible getting transferred to the output...not the clamp! Also, you might want to look into what clamping voltage you design the clamp to operate at. If the clamping voltage is too close to the drain pin voltage during normal operating conditions...you end up with a clamp that is operating all the time and dissipating excess power. Raising the clamp voltage higher can significantly drop your clamp power dissipation, provided you've made sure that BVDSS for the TopSwitch MOSFET isn't being exceeded, especially during line voltage surge events.


In PI Expert, you should be able to get the software to work with the basic input/output specs you gave me. You'll get lots of warnings because you're right on the edge of the maximum amount of power you can deliver with TopSwitch. You'll need to play around with different device packages...but a few of them should be able to get up to 322 watts. Even if the software doesn't give you a complete design, it might serve as a bit of a sanity check for the design you've done on paper. If you give me some more of the particulars of your design, transformer design, component values, etc...I might be able to start a PI Expert design for you so that you can experiment with the design.


Let me know if I can be of any other help.

-The Traveler