What is the working principle and function of a fast recovery diode? — SUNMATE

What is the working principle and function of a fast recovery diode?

Fast Recovery Diode (FRD) is a semiconductor diode with good switching characteristics and short reverse recovery time. It is mainly used in electronic circuits such as switching power supplies, PWM pulse width modulators, frequency converters, etc., as a high-frequency rectifier diode, freewheeling diode, or damping diode. The internal structure of a fast recovery diode is different from that of a regular PN junction diode. It belongs to the PIN junction type diode, which adds a base region I between the P-type silicon material and the N-type silicon material, forming a PIN silicon chip. Due to the thin base region and low reverse recovery charge, the fast recovery diode has a shorter reverse recovery time, lower forward voltage drop, and higher reverse breakdown voltage (withstand voltage).

Working principle of fast recovery diode

The internal structure of the fast recovery diode is the addition of base region I between P-type silicon material and N-type silicon material, forming a PIN silicon chip. Due to the thin base region, the reverse recovery charge is very small, which not only greatly reduces the TRR value, but also reduces the transient forward voltage drop, enabling the tube to withstand a high reverse operating voltage.

The reverse recovery time of fast recovery diodes is generally several hundred nanoseconds, with a forward voltage drop of about 0.6V, a forward current of several amperes to several thousand amperes, and a peak reverse voltage of several hundred to several thousand volts. The reverse recovery charge of the ultrafast recovery diode is further reduced, allowing its trr to be as low as tens of nanoseconds. Fast recovery and ultra fast recovery diodes below 20A are mostly packaged in TO-220 format.

When negative voltage (or zero bias) is applied, the fast recovery diode is equivalent to a capacitor+resistor; When a positive voltage is applied, the fast recovery diode is equivalent to a small resistance. By changing the structural size and selecting the parameters of the fast recovery diode, the reflection phase (reference phase) of the short-circuit stepped ridge waveguide is the same as that of the short-circuit waveguide controlled by a positive voltage PIN tube. The reflection phase of the short-circuit waveguide controlled by a fast recovery diode with negative voltage (or 0 bias) is also required to be opposite to the standard phase (between -164 ° and+164 °).

Fast recovery diode function (in DC circuits)

Fast recovery diode, characterized by high voltage resistance and low leakage current during reverse blocking, and high current resistance in forward low-pass state. Due to its use as a switch, it is generally required to have a fast switching speed. In addition, selecting the characteristics of the freewheeling diode appropriately, especially the reverse recovery characteristics, such as reverse recovery time and reverse recovery softness, can significantly reduce the power consumption of switching devices, diodes, and other circuit components, and reduce voltage spikes and electromagnetic interference caused by the freewheeling diode, thereby minimizing or even removing the absorption circuit as much as possible.

Generally speaking, the forward voltage drop of fast recovery diodes is small, around 0.4V, while that of ordinary silicon tubes is around 0.6V. Fast recovery diodes are only used to reduce losses.

If the reverse breakdown voltage of the fast recovery diode is 40V, it can quickly recover after reverse breakdown; If the reverse breakdown voltage of the fast recovery diode is 1000V, there is no reverse