Snubber calculation
Dear all,
How can we design a practical snubber for flyback converter? RC/RCD etc..
As you know application notes assumes all the leakage energy will dissipate in the snubber and if we make design due to this we achieve big snubber power loss which is not feasible.
For example for 50W SMPS according to snubber design datasheet 6W snubber rqcuired which makes %12 loss in the snubber.. Also this design requires big power resistors in order not to increase in temperature so the size of them very big..
Is there any practical design for the snubber? which is more realistic..
Comments
Dear Terry,
First of all ı could not find any application note related with snubber calculation in PI website.. Bur there are some application notes in the area like
http://www.fairchildsemi.com/an/AN/AN-4147.pdf
I also find different Aplication notes from internet and all of them smilar..
According th this datasheet all the leakage energy must be dissipated in snubber and formula;
Psnubber = 1/2 * I peak^2 * Lleakage* Vsnubber/(Vsnubber-Vreflected)* fswitching
So for my design
Leakage is 7uH and I peak 3.06A , Vsnubber is 200V ,Vor 80V and fs 67kHz...I calculate Ps nubber around 3.6W.. which is very much..
But when I check your referance designs I found very similar design DER218, Leakage is 5e-6, I peak 3.55, Vsnubber is 200V(TVS200V ) and Vor 90 V. But in this design sheer PI use 1W resistance and MUR160 1A diode. so both diode rating below peak current 3.55A and snubber power is small..
In additon to this again refer to snubber A4147 datasheet if we use 100K resistance snubber voltage must be very big than 200V.. so I don't understand how to design snubber...
In my circuit if I use 47K 2W parallel with 2n2 kV and P6KE200A P6KE200A sometimes burns..
Is there any datasheet or calculation method for snubber in PI?
Is there any suggestion or solution ?
Hi:
Would you please let me know which application note that you are talking about? The leakage energy for a 50Watts desing is certainly not 12% (6W), how did you calculate with this number? What is the leakage inductance measured on your transformer? Please give me more information that I can assit you further.