Non-dissipative clamp for flyback converter

[ysba]

Hi,

Has anyone used a non-dissipative clamp for flyback converters? I'm using a circuit like this, but I found few information about how many turns must be placed in the snubber winding. I saw only a piece of a text, saying that it must have the same number turns of primary winding.

I mounted the circuit, and it clamps the votlage spike, but I'd like to reduce its value yet more. My question is if I get a better result changing the number of snubber winding turns.

Also, I figured in practice that the value of the first VDS spike at mosfet's turn-off is strongly influenced by snubber's diode recover time. Putting in values, the input voltage plus the secondary reflected voltage is 150V. Using this non-dissipative snubber, the spike reaches 200V. I'd like to know if this value would be less using a better diode. Now I'm using a MURA120, with 35ns recovering time.

Thanks.

 

[mtwieg]

For a circuit like that the performance is going to be limited by the coupling between the primary and the and snubber winding. Use bifilar windings, and if that isn't good enough you need another circuit entirely.