TIDA-01623: The difference between active flyback and QR flyback

Hi 

the spike on Vds caused by leakage inductance will be absorbed in clamp capacitor in ACF, and and will be recycled to secondary eventually. so the spike will not be seen on Vds compared with QR flyback, 

for ZVS, since QR will turn on at the vally of natural ring at Vds, so it might not be able to achieve ZVS at certain conditions, such as High line input, but for ACF, since the bidirectional switch on high side implemented, it will provide a path to generate a negative magnetizing current to discharge Vds Coss before main low side switch on, thus ZVS can be achieved. 

BR

Max

Hi 

I think you can refer some paper for ACF first before we go details. as the above already address the question you have,

the two bridge rectifies is just for thermal concern, if you have good thermal spreading condition, you can use one for sure

Hi Fu

QR can absorb the voltage spike a little, but has no path for recycle the leakage energy. but dissipate it completely.

QR can achieve ZVS at low line with natural switching, but not able to achieve natural switching at high line

for ACF, since there is a bi directional switch, so it provide a path for recycling the leakage as well as ZVS   

Hi Xu

this is just like conventional flyback with RCD clamp

Hi Xu,

it is called resistor capacitor clamp. which is a common clamp circuit for flyback