With the development of power electronics technology, the applications of various frequency conversion circuits and chopper circuits are expanding. Whether the main circuit of these power electronics circuits is thyristor with commutation switching off or new power electronics devices with self-switching ability, such as GTO, MCT, IGBT, etc., all need a fast parallel connection. The electrode can reduce the charging time of capacitor by reactive current in the load, and suppress the high voltage induced by the instantaneous reverse of the load current. Due to the continuous improvement of frequency and performance of these power electronic devices, in order to match the switching process, the diode must have fast switching-on and high-speed switching-off capabilities, i.e., short reverse recovery time rr, small reverse recovery current IRRM and soft recovery characteristics.

In high voltage and high current circuit, the traditional PIN diode has good reverse voltage withstanding performance, and when it is in the forward direction, it can turn on a larger current at a very low voltage, showing a low resistance state. However, the existence of a few carriers with large forward injection makes the minority carrier lifetime longer and the switching speed of the diode correspondingly lower. In order to improve the switching speed of the diode, the minority carrier lifetime can be reduced by doping heavy metal impurities and irradiating by electrons, but this will cause the hard recovery characteristics of the diode to varying degrees. The high induction voltage has an important influence on the normal operation of the whole circuit.

1: Working Principle and Influencing Factors

Diodes with very short recovery process, especially those with very short reverse recovery process, are called Fast Recovery Diodes. High-frequency power electronic circuits require not only a fast recovery diode with good forward recovery characteristics, i.e., small forward transient voltage drop and short recovery time, but also a good reverse recovery characteristics, i.e., short reverse recovery time, less reverse recovery charge and soft recovery characteristics.

Opening Characteristic

There is also a process of diode switching on. In the initial stage of switching on, there is a high transient voltage drop. After a certain period of time, the diode can be in a stable state and has a small tube voltage drop. That is to say, the diode shows obvious "inductance effect" in the initial stage of switching on, and can not respond to the change of forward current immediately. During the forward recovery time, the on-going diode has a much larger peak voltage UFP than the steady state. When the forward current rise rate exceeds 50 A/s, there is a high transient voltage drop in some high voltage diodes. This concept is very important in the fast application of buffer circuits.

In addition to the internal mechanism of the device, the inductance effect of the diode is related to the length of the lead and the magnetic material used in the device package. Inductance effect is most sensitive to the change rate of current, so the higher the rise rate of diode current diF/dt, the higher the peak voltage UFP and the longer the forward recovery time.