Basic question on diode turn-off flyback converter

[LaMontagne]

Good morning,

I have a small problem understanding the turn-off of diodes. I am thinking in particular about the turn-off of the secondary side rectifier diode of the flyback converter.

Until now, I assumed that if the diode current reaches zero naturally without any forced commutation, one can not observe any reverse recovery effects and the diode blocks when the diode current reaches zero.

However as I am doing some SPICE simulations, there is clearly a reverse recovery current leading to a turn-off delay. A diode having fast recovery improves clearly the performance (current blocks instantly).

I would appreciate if you could clarify my problem of understanding! Thanks

 

[abhinand rd]

In pratical diodes except ultra fast ones, there is certain reverse recovery effect observed and diode doesnt block at the instant the diode current reaches zero. its information can be obtained by Qrr and Trr from datasheets.