Fast Recovery Diode: How does it Work? And its characteristics


Fast recovery diode is a PN junction type diode which possesses short reverse recovery time for rectification purpose at high frequency. A quick recovery time is required for rectification of high frequency signal. The diode has ultra-high switching speed and it is use in rectifier. The conventional diodes has high recovery time which is not suitable for high frequency. For high frequency fast recovery diodes are use.

What is a Fast Recovery Diode?

A fast recovery diodes is semiconductor diode which has short reverse recovery time than conventional diodes. It is suitable for high frequency ratification applications. Due to short reverse recovery time it is also known as fast diode or fast switching. It can operate switching up to 100 kHz.

When the diodes is in reverse bias, the diodes does not withstand voltage until it enters reverse bias. In reverse bias, the current flow for a specific time. And this specific time is called reverse recovery time (TRR).

The reverse recovery time of fast recovery diode is lie in between tens of nano seconds to 100 nano seconds. While the reverse recovery time for normal PN junction diodes lie in between a few micro-second to tens of micro-second. Hence the reverse recovery time (TRR) of fast recovery diodes is low as compare to conventional diode.

Fast recovery diode symbol

The fast recovery diodes is similar to normal conventional diodes. The major difference is fast diode use Gold (Au) in semiconductor. This increase numerical value of recombination centres due to which the lifetime of charge carriers decreases.


Construction of Fast Recovery Diode

The construction of fast recovery diode is similar to conventional PN junction diode. The major difference of conventional diode to PN junction diode is the presence of recombination centres. In fast recovery diodes construction, Gold (Au) is use in semiconductor material. This leads to augmentation in the numerical value of recombination centres. It decreases the lifetime of charge carriers.


The addition of Gold (Au) in semiconductor, the recovery time decreases (about 0.1ns). The recovery time of silicon is 1-5 ns. This shows the addition of materials like gold decreases the recovery time.


Typical characteristics

Withstand voltage (VRM) → High voltages such as 600 V, 800 V and 1000 V
Forward voltage (VF)   Approximately 1.3 to 3.6 V
Reverse current (IR) → Extremely small from several μA to tens of μA
Reverse recovery time (trr) → Approximately tens of nS to 100 nS
Application → Rectifying high voltage switching circuits (such as PFC)

It is use for select the diode according to each application, because the smaller the reverse recovery time is made, the larger the VF becomes.

How does a Fast Recovery Diode work?

Consider the low frequency of AC signal is use where low DC is required. We need a rectifier that converts alternation current to direct current. If we use conventional diode for rectifying AC signal, then it may rectify efficiently.


In low frequency the time period is high. The high time period will take more time to complete one cycle. Therefore, the conventional diode has enough time to change the voltage polarity from one positive to negative or vice versa.

For high frequency signal, we know the frequency is inversely proportional to time. The high frequency shows the minimal time interval and signal will take a minimal time to complete the cycle. For minimal time the conventional diode is not suitable because it take more time to change voltage polarity. So, we need that type of semiconductor device which has a low reverse recovery time.

The material of conventional diode is Gallium-Arsenide (GaAs) but fast recovery diode, the gold (Au) is added with Gallium-Arsenide. By adding gold in semiconductor material to reduce the reverse recovery time. And it increases the switching speed from positive to negative half cycle. This is useful for high-frequency applications.

Recovery characteristics of diode


Relationship between forward current (IF) and reverse recovery time (trr)

When diode is forward bias, the current start flow through diode and it is called forward current (IF). And when the transform forward to reverse bias some amount of current will flow through diode and this current is called recovery time (TRR). It is in order of micro ampere. The diode only pass forward currant and block reverse current.

In forward bias, the electron and holes pass through junction and move opposite side area. But in reverse bias electron and hole cannot move opposite side and create a depletion layer.

In reverse bias, the holes and electron move back to their side. The comparison in between large recovery time and small forward current.

When forward current is small


When forward current is large


How to improve trr


Heavy metal is diffused or an electron beam is irradiated onto the diode with a p-n junction to create a carrier trap in order to catch holes while they are going back. The trr is improved by 2 to 3 digits, but the VF becomes larger as a result.

Classification of Fast recovery Diode

The fast recovery diodes is classified into two categories on the basis of its construction. One is form by diffusion of P and N diffusion and other is from by metal semiconductor. The metal semiconductor possesses ultra high switching speed because metal semiconductor has only majority carrier. There is negligible effect of minority charge carrier storage.

It is also classified on the basis of packaging type, operating voltage and maximum average rectified current.

Fast Recovery vs. Schottky Diodes

Schottky diode made by junction of semiconductors with metal (such as gold, tungsten, platinum, molybdenum, chromium).

Let’s understand the difference between a Schottky diode and fast recovery diode.

 Parameter Fast recovery diode Schottky diode
Construction Similar to a conventional diode, it has a PN junction. It is from by the contact between metal and semiconductor and this barrier is called schottky barrier.
Material used The gold is added in semiconductor material, It has N-type semiconductor material and metal are used to form a Schottky barrier.
Power consumption High Less
Forward voltage drops 0.5-2 V 0.4-1 V
Reverse withstand voltage Less than 1200 V Less than 150 V
Reverse recovery time (TRR) Tens of nano-second to 100 nano-second. Compared to the Schottky diodes, reverse recovery time is high. But it is very low compared to convention diode. Less than 20 nano-second.
Application It is use in Rectifier, Analog and digital communication circuit Radio signal detector, industrial and commercial purpose. Voltage clamping, SMPS and solar cell, discharge, reverse current, protection, Radiofrequency (RF), and Detector diode.

Applications of a Fast Recovery Diode

The applications of a fast recovery diodes are given below:

  • It is use in high-frequency rectifier.
  • AC to DC converters and inverters.
  • Detect high-frequency RF waves.
  • Switching power supplies.
  • Industrial and commercial electronics circuits.
  • In modulation purposes, it is used in various analog and digital commutation circuits.
  • Fast recovery diodes is in Power factor correction and power factor controller

Advantages of a Fast Recovery Diode

The fast recovery diode advantages is described below:

  • High switching speed
  • It has Low reverse recovery time
  • Good efficiency
  • Low power loss

Disadvantages of a Fast Recovery Diode

When recombination centers are increased by adding gold in a fast recovery diode, it possesses a high reverse current.

Fast recovery diode list

For ONSEMI Fast / Ultrafast Diode, 600 V, 1 A, Single, 1.7 V, 35 ns, 30 A

Repetitive Reverse Voltage Vrrm Max 600V
Forward Current If(AV) 1A
Diode Configuration Single
Forward Voltage VF Max 1.7V
Reverse Recovery Time trr Max 35ns

Fast recovery diode vs standard

The fast recovery diodes is similar to conventional PN junction diode. The only difference is in construction between PN junction is the presence of recombination centres. But in fast recovery diode is addition of Gold (Au) in semiconductor material.

Also read:- PIN diode, Half wave rectifier, Full wave rectifier, Alternation current.

People also ask fast recovery diode (FRD)

What is fast recovery diode?

The fast recovery diodes is also called fast switching diodes. It is semiconductor device with short reverse recovery time. Because it has low recovery time as compare with convention diodes. It is use in high frequency rectification application.

Is Schottky diode a fast recovery diode?

Schottky barrier diodes (SBD) are not a convention PN diodes. The material is use metal and N semiconductor. Fast-recovery diodes (FRDs) are PN junction diodes, but are fast diodes with a greatly improved trr.

What is fast switching diode?

A fast recovery diode is semiconductor diodes which has short reverse recovery time than conventional diodes. It is use in high frequency ratification applications


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