Flyback Converter-Need Help
hi all,
we are designing flyback converter with following parameter:
input voltage:230V
output voltage:5v
frequancy:70Khz
Diode: Fast Recovery Diode B860
transformer: primary turns:88
secondary turns:2
problem is that switch or transformer get heated when we apply voltage above 90(at that time current is 0.95A). we intechange secondary terminal also(strange thing is that we got output voltage for both the case when applied voltage is low). we Increase Frequancy up to 120Khz & duty ratio 30 to 70% to avoid core saturation. but nothing improvement.
I have use so many MOSFET 220V to 1000V(IRFP250N IRF 450 then 2SK1120) but all fail.
I have add 1k resistor between gate & Source.
also add RCD snubber to clamp but nothing could be help.
every time either MOSFET or transformer get heated when apply voltage above 80to 100V.
I checked Vdss voltage it was 40 V when my o/p is around 0.001V.
we have made hand made transformer with air-gap 2-3mm
plz help to solve the problem