In the RCD clamp circuit, which diode is slow or fast? — SUNMATE

In the RCD clamp circuit, which diode is slow or fast?

RCD circuit is often used in some occasions that need clamping, such as voltage clamping of flyback primary MOS and voltage clamping of secondary rectifier. Some technical documents say that the slow recovery transistor should be used because the reverse recovery time of the slow recovery transistor is relatively long, so part of the energy in the clamping capacitor will be fed back to the circuit during the reverse recovery of the diode, so that the loss of the whole RCD circuit can be reduced. However, this is only suitable for occasions with low current and low di / dt. For example, the primary clamping circuit of low-power flyback. However, it is not suitable for clamping occasions with high current and high di / DT, such as the secondary clamping circuit of power supply with high current output. Because the slow recovery tube will produce a high conduction voltage drop peak when it is turned on, which makes it impossible to clamp the peak voltage although the voltage on the clamping capacitor is very low. So we should choose Schottky diode and so on.