HELP NEEDED to calculate a snubber for the primary of smps

Silvio

Active member
Hi, can anybody help me calculate the values of a snubber needed for the primary winding of a half bridge smps?
At the moment I have 680pf 1kv with a series resistor of 150 ohms at 3watts but its getting rather hot!

Input voltage = 230 volts AC
Input dc voltage at transformer Primary is 155 Vdc
Output voltage is 45-0-45 volts dc
transformer used is EI 40
calculated output power is 350 - 400 watts
operating frequency is 75Khz
Mosfets used are IRF 740
Drive circuit with IR2153
duty cycle 50%

HELP IS GREATLY APPRECIATED.
 

Silvio

Active member
Thanks very much for your help. It is a bit late though as I figured it out by trial and error and found the best value to be 150 ohms and 220nf gave me the best results

regards Silvio
 
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