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FRDs (Fast Recovery Diodes)

Download "Chapter II : Diodes" (PDF:895KB)

The structure and function of fast recovery diodes (FRDs) are the same as those of rectifier diodes. Rectifier diodes are used for low-frequency applications below 500 Hz, whereas FRDs are used for high-frequency switching from a few kHz to 100 kHz. Therefore, the reverse recovery time (t_rr) of the diode characteristic, which is important for high-speed switching, is short. FRDs are also referred to as S-FRDs, HEDs, etc. according to the trr value.
t_rr of a general rectifier diode is several μs to several tens of μs. On the other hand, t_rr of an FRD is several tens of ns to several hundred ns and is about 1/100 of that of the rectifier diode. It is used in switching power supplies, inverters, DC/DC converters, etc.

Fig. 2-3(a) Example of diode switching waveform and loss

Fig. 2-3(b) Comparison of t_rr between general-purpose rectifier and FRD

The loss due to t_rr (reverse recovery loss) is negligible when the frequency is low, but this loss increases with frequency, and it cannot be ignored if it becomes several kHz or more.