The RC peak a4ption problem of Flyback's secondary rectifier diode 4

The reverse recovery of rectifier tubes only occurs in continuous operation mode, diode and there will be no reverse recovery problem of rectifier tubes in the power topology of intermittent operation mode;

The capacitance effect of the rectifier tube and the secondary stray capacitance and secondary leakage inductance can cause oscillation. This oscillation is manifested as the resonance of the transformer output terminal+output voltage through the secondary leakage inductance and the stray capacitance of the rectifier tube under the influence of the large dv/dt (voltage change rate between the transformer and the rectifier tube) and the reverse recovery current of the diode (continuous mode), thereby causing a peak in the reverse voltage of the rectifier tube.diode

Simply put, reverse recovery of a diode refers to a dynamic process in which a conducting diode transitions from a conducting state to a reverse cut-off state. There are two prerequisites: the diode must have a certain forward current before reverse cut-off (the current size affects the maximum peak current and recovery time of reverse recovery, and the already cut-off state is not included, so only continuous mode has reverse recovery problems); To ensure that the diode quickly enters the cutoff state, a reverse voltage is applied across the diode (the magnitude of this reverse voltage also affects the known reverse recovery current and recovery time of the diode). So to see if there is a reverse recovery issue, you can compare whether it meets these two conditions.diode

The advantage of a quasi resonant circuit is that it changes the maximum terminal voltage NUo+Uo of the intermittent mode rectifier diode to NUo Uo, reducing the voltage change rate of the rectifier diode when the primary MOS transistor is turned on, thereby reducing the excitation source of leakage inductance oscillation and reducing the oscillation peak generated. If the amplitude does not affect the voltage withstand safety of the rectifier diode, it can completely eliminate the absorption circuit such as RC.diode