Working principle of fast recovery diode

What is 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, and frequency converters, 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 P-type silicon material and N-type silicon material to form a PIN silicon wafer. Due to the thin base region and small reverse recovery charge, fast recovery diodes have a shorter reverse recovery time, lower forward voltage drop, and higher reverse breakdown voltage (withstand voltage value).

Working principle of fast recovery diode

The internal structure of the fast recovery diode is to add a base region I between P-type silicon material and N-type silicon material, forming a PIN silicon wafer. 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, allowing the diode to withstand high reverse operating voltages.

The reverse recovery time of a fast recovery diode is generally several hundred nanoseconds, the forward voltage drop is about 0.6V, the forward current is several amperes to several thousand amperes, and the peak reverse voltage can reach 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.

When a 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 resistor. By changing the structural dimensions and selecting the parameters of the fast recovery diode, the reflection phase (reference phase) of the short-circuit stepped ridge waveguide is made the same as that of the short-circuit waveguide controlled by the PIN diode with positive voltage. It is also required that the reflection phase of the short-circuit waveguide controlled by a fast recovery diode with negative voltage (or 0 bias) be opposite to the standard phase (between -164 ° and+164 °).

Fast recovery diode function (in DC circuits)

Fast recovery diode has the characteristics of high 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 the voltage spikes and electromagnetic interference caused by the freewheeling diode, thereby minimizing or even removing the absorption circuit.

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

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 problem of reverse breakdown, so this can be ignored in DC circuits.