Fly-back Power Supply: UCC28C44, CS20N65 MOSFET, Voltage Clamping Circuit Burns

Good morning~all

I am involving in a project about fly-back switch power,I am not professional so here I am.

I have drawn the schematic diagram PCB and tried to weld and debug.Now I met some problems in the switch power.The outputted voltage is right.However, the voltage clamping circuit and rush absorbing circuit burned obviously after working for a long time. At the same time, the transformer made a sound.The basic situations are as following:

Fly-back switch power : the switch frequency is 60KHz, the UCC28C44 is controlled by PWM, the outputted power < 50w,the voltage of main power is 320V DC (220 AC  rectification and filtering). The schematic diagram is given below.

 

R167=R87=7.5K (2512)    R169=10 (2512)    C133=4700pF    C134=680pF    R171=R88=750    R166=22   

 MOSFET model:CS20N65

Mosfet wave is given below.

The blue is the controlling signal. The yellow is the Mosfet drain voltage. When closing the Mosfet,the drain voltage will reach 500V ,then down to 300V after a period of time.I would like to ask:


.Does the wave have porblems ? How to improve the circuit and down the Mosfet drain voltage?
. The transformer always made a noise. How to solve it ?


Please help me. Thank you.

Hi, ling ling

I think instead of R31 you can go for a preset 4.7k to 5k and vary the gate voltage by reducing the gate voltage of the mosfet you can control the mos drain voltage, noise may be either due to the freq set of 60 hz or you may be overloading one of the sec winding supply of the smps transformer try adding low value resistor to the sec windings to limit the current one by one to find out which winding is overloaded. review my rating good luck.