How to choose the reverse recovery time of the rectifier diode for the secondary output of a switching power supply

How to choose the reverse recovery time of the rectifier diode for the secondary output of a switching power supply? Choose current and voltage, as long as the fast recovery diode can reach or exceed the operating frequency of the switching power supply. In modern pulse circuits, transistors or diodes are widely used as switches, or logic integrated circuits mainly composed of them are used. As a switch application, diodes mainly utilize their on (low resistance) and off (high resistance) characteristics, that is, the switching effect of diodes on forward and reverse currents.

The difference between diodes and general switches is that the "on" and "off" states are determined by the polarity of the applied voltage, and the "on" state has a small voltage drop Vf, while the "off" state has a small current I0. When the voltage changes from forward to reverse, the current does not immediately become (- I0), But during a period of time ts, the reverse current remains high and the diode does not turn off. After passing through ts, the reverse current gradually decreases, and after tf time, the current of the diode becomes (- I0). ts is called the storage time, and tf is called the decay time. Tr=ts+tf is called the reverse recovery time, and the above process is called the reverse recovery process.