The RC peak absorption problem of Flyback's secondary rectifier diode 1

When discussing the RC peak absorption problem of the secondary side rectifier diode in Flyback, it is found that using RCD absorption is more effective than using RC absorption in dealing with such peak problems. Using RCD absorption can lower the peak voltage of the rectifier tube (with reasonable parameter matching, it can completely absorb and almost no peak voltage can be seen), and the absorption loss is also smaller.diode

Voltage waveform of rectifier diode (RC absorption)

Voltage waveform of rectifier diode (RCD absorption)

From these two simulation images, it can be seen that the absorption effect is comparable. If the high voltage drop when the diode is turned on is not considered, it can be considered that the absorption is complete.

After the experiment, you should be pleasantly surprised that the diode can be made of surface mount (fast switching diode, if the parameters are appropriate, 1N4148 is good), and both resistors and capacitors can be made of surface mount.

The RCD absorption design here can be considered as follows: in order to absorb the oscillation peak, C should have sufficient capacitance. After absorbing the peak energy, the voltage on the capacitor will not be too high. In order to balance the energy on the capacitor, resistor R needs to consume the leakage inductance energy stored in capacitor C. Therefore, the ideal parameter combination is that the energy consumed by the resistor is exactly equal to the energy in the leakage inductance peak (at this time, the voltage at the terminal of capacitor C is exactly equal to Uin/N+Uo). Because there are many uncertain factors in the leakage inductance peak energy, the calculation method is difficult to be effective. Therefore, the following introduces an experimental method to designdiode