What are Fast Recovery Diodes (FRD)? How to Select FRD?

 Fast Recovery Diodes (FRDs) are high-speed diodes designed to have a quick recovery time when switching from the conducting state to the blocking state. These diodes are commonly used in applications where rapid switching is required, such as in power converters, inverters, and switching power supplies.

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)

Soft recovery and hard recovery

When the recovery current restores too suddenly, it produces more noise. As a result, the trr must not only be small but it must restore softly or smoothly.

Numbers 1 and 3 below may appear to have the same trr in the catalogue, but both the loss and noise are quite different. In addition, the number 2 appears to be extremely good when looking at the catalogue, but it produces a large noise.

When selecting FRDs for a particular application, several parameters should be considered:

Recovery Time: 

This is a critical parameter and refers to the time it takes for the diode to switch from the conducting state to the blocking state. A fast recovery time is desirable for applications requiring high-frequency switching.

Forward Voltage Drop: 

This parameter represents the voltage drop across the diode when it is conducting current. Lower forward voltage drop leads to reduced power dissipation and improved efficiency.

Reverse Recovery Charge: 

This parameter quantifies the charge stored within the diode during the recovery process. A lower reverse recovery charge is preferred as it reduces switching losses.

Reverse Recovery Time: 

This is the time it takes for the diode to recover from the blocking state to the conducting state. A shorter reverse recovery time is desired to minimize the period of high reverse voltage and reduce power losses.

Reverse Voltage: 

This parameter indicates the maximum voltage that the diode can withstand in the reverse direction. It is crucial to select a diode with a reverse voltage rating higher than the application's requirements.

Current Rating:

 The current rating specifies the maximum current that the diode can handle without being damaged. It is important to choose a diode with a current rating higher than the expected operating current.

Package Type: 

The physical package of the FRD is also a consideration, as it should be compatible with the application's mounting and assembly requirements.

These parameters are crucial in selecting the appropriate FRD for a specific application, and manufacturers' datasheets provide detailed information to help engineers make informed decisions.