Fast Recovery Diode

A fast recovery diode (FRD) is a type of diode with a short reverse recovery time (Trr) that is used for high-frequency switching!

The structure and function of an FRD is the same as that of a rectifier diode.

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 (Trr) 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.

The trr of a general rectifier diode is several μs to several tens of μs. On the other hand, Trr 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.

In other words, FRD is a diode with a p-n junction is designed to make the reverse recovery time (Trr) smaller and is also called a high-speed diode.

Compared to general rectifying diodes (standard recovery diodes), the Trr is 2 to 3 digits smaller because the FRD is designed with a switching power supply to rectify high frequencies of tens of kHz or hundreds of kHz.

So, FRD stands for fast recovery diode. Such a high-speed diode offers high-speed support and generally have a Trr of approximately 50 to 100 ns.

Note, with a VF (forward voltage) of approximately 1.5 V, it is rather large when compared to general rectifying diodes (the smaller the reverse recovery time is made, the larger the forward voltage becomes).

On the other hand, general rectifier diodes are low-speed p-n diodes with large trr and small VF. These diodes are designed for commercial frequencies such as 50/60 Hz, and are not used in fast switching circuits.

Even among the fast recovery diodes, Ultra Fast Recovery Diode is a component designed specifically for speed. In this case, the Trr is approximately 25 ns, which is extremely small, but the VF is quite large at 3 to 3.6 V.

Now see the PDF datasheet of the FR107 1A Fast Recovery Diode https://www.diodes.com/assets/Datasheets/products_inactive_data/ds26001.pdf

To sum-up, diodes can be subdivided into two main classes: Rectifier diodes (standard recovery) and fast diodes.

Rectifier diodes are generally used for conversion of alternating current to direct current (AC to DC). While optimized for low conduction losses, rectifier diodes withstand only moderate dynamic stress in transition from conducting to the blocking state.

Fast diodes, on the other hand, are companion devices to switches in DC to AC conversion. Fast diodes are optimized to accept high dynamic stress (fast transition from conducting to blocking state). However, they generally have higher conduction losses than rectifier diodes.

(thanks to https://www.shindengen.com/ , https://www.hitachienergy.com/in/en , &  https://www.global.toshiba/ww/top.html)