Snubber for flyback transformer.

[I_think]

Ref: https://www.edaboard.com/threads/159495/#post678002

Some doubts that still aren't clear are.

1) Do we need snubber ckt across fet with internal protection diode?

2) With flyback transformer, the flyback (or back emf) is in inverse direction with the input. then why is required fet voltage calculated as

flyback voltage + line voltage ?

3) Why RCD, Not just Diode, Like using freeweeling diode?

 

[FvM]

Do we need snubber ckt across fet with internal protection diode?

If you refer to the controlled avalanche breakdown capability of modern FETs, it can be utilized instead of a snubber. But then you get the power dissipation inside the transistor.

flyback voltage + line voltage

Because the flyback voltage across the transformer is inverse to the input voltage.

Why RCD, Not just Diode, Like using freeweeling diode?

Usually, a flyback converter is intend to generate output voltage at the secondary, not clamp it to 0.7 V. In addition, you'll notice that duty cycle is related to forward/flyback voltage ratio.

 

[Sanchayan]

https://focus.ti.com/docs/training/catalog/events/event.jhtml?sku=SEM411001

Refer Topics 1 and Topics 2.