Fast Recovery and Standard Recovery Diodes

A fast recovery diode is a diode that has a quick recovery time. This blog explains the fundamentals of the fast recovery diode and standard recovery diode, including its theory, functionality, construction, and applications. 

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Fast recovery diode

A fast recovery diode is a diode that has a quick recovery time. When dealing with AC signals, such as rectifying them, a diode must recover from one signal to the next after a finite period of time. A typical diode recovers in a few microseconds (µs),  This is fine for low-frequency applications. On the other hand, a  fast recovery diode recovers in nanoseconds (ns).  this is important In very high-frequency applications. A Fast Recovery Diode (FRD) is a device that possesses a short reverse recovery time for rectification purpose at high frequency. The rectification of a high-frequency AC signal requires a quick recovery time. Because of its fast switching speed, diodes are commonly utilized in rectifiers.

CONSTRUCTION

The fast recovery diode is constructed in the same way as a regular diode is constructed. The major difference in construction between these diodes and conventional diodes is the presence of recombination centres. Gold (Au) is added to the semiconductor material in fast recovery diodes. 

Gallium Arsenide is the semiconductor material used in these diodes (GaAs). The recovery time is reduced when gold (Au) is added to the semiconductor material (about 0.1ns). In the case of silicon, the recovery time is 1-5 ns. As a result, it's clear that adding materials like gold decreases the fast recovery time.

WORKING

Consider a low-frequency AC signal, now if it is used in an application where low voltage DC is required. In this case, a rectifier is required to convert AC to DC. If we use a conventional diode to rectify the AC signal, it will probably rectify efficiently.

However, the diode may not work effectively if we want to rectify a high-frequency AC signal. The reason for this is that at low frequencies, the width of signal pulses is more, allowing a diode to change its state between the positive and negative half of the cycle insufficient time. It can be understood like the signal is striking slowly. As a result, the diode easily switches between positive and negative half signals. But this is not the case in which a high-frequency signal strikes a diode for rectification. 

 The frequency of the signal is inversely proportional to the time time period of the signal, the time period decreases as the frequency of the signal increases. As a result, at high frequencies, the pulse width becomes small.

As a result, the AC signal rapidly switches from positive to negative half. In this situation, if we want to rectify the signal, we need a diode with a low recovery time that can quickly switch from the positive to the negative half of the signal. The diode's rectification speed must match the frequency of the AC signal.

The reverse recovery time is reduced by adding gold as a semiconductor material. Hence, it can switch fast from positive half cycle to negative half cycle. It can be used in high-frequency applications.

Fast recovery diode chart

Below shows the difference in recovery time between a fast recovery diode and a standard diode:

Fast recovery diodes have a lower reverse recovery time than normal diodes, making them more suitable for high-frequency rectification. Fast recovery diodes are commonly used in high-frequency applications because they can be turned off very quickly. In high-frequency switching up to 100 kHz, fast recovery diodes are used.

The diode does not withstand voltage until it enters reverse bias when voltage is applied in the opposite direction. The current flow for a specific time in reverse bias conditions. This time is known as reverse recovery time (TRR). A fast recovery diode, reverse recovery time (TRR) is lies between the tens of nanoseconds to 100 nanoseconds. A conventional diode's reverse recovery time lies between a few microseconds to tens of microseconds.

Hence the fast recovery diode has a reverse recovery time several orders of magnitude faster than a conventional diode. The major problem with the conventional diode is that they possess a quite high recovery time. Due to which the rectification of high frequency is not possible with a conventional diode.

Advantages of Fast Recovery Diode

• Ultrahigh Switching Speed

• Low reverse recovery time

• Improved efficiency as compared to conventional diodes.

• Reduced loss

Applications of Fast Recovery Diode

• Rectifier: These diodes are used in rectifiers especially for high-frequency rectification.

• Industrial and commercial areas: They are used in electronics circuits in various industries and the automobile sector.

• Radio signal detectors: They are used in radio signal detectors to detect high-frequency RF waves.

• Analog and Digital communication Circuits: In analog and digital communication circuits these diodes are extensively used for rectification and modulation purposes.

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SOME COMMON FAST RECOVERY DIODE

• FR207 Diode-

  For FR207 Diode, the maximum current carrying capacity is 2A it withstands peaks up to 70A. Hence we can use this in circuits that are designed for less than 2A. The reverse current is 5uA which is negligible.

• FR607 Diode- 6.0A Fast Recovery Rectifier- For FR607 Diode, the maximum current carrying capacity is 6A it withstands peaks up to 200A. Hence we can use this in circuits that are designed for less than 6A. The reverse current is 10uA which is negligible.

• SF28 Diode&#; 2A V Super Fast Rectifier Diode- For SF28 Diode, the maximum current carrying capacity is 2A it withstands peaks up to 75A. Hence we can use this in circuits that are designed for less than 2A. The reverse current is 20uA which is negligible. 

• SF58 Diode &#; 5A V Super Fast Rectifier Diode-  For SF58 Diode, the maximum current carrying capacity is 5A it withstands peaks up to 135A. Hence we can use this in circuits that are designed for less than 5A. The reverse current is 10uA which is negligible. 

STANDARD RECOVERY DIODE

Standard recovery diode is a basic P-N Junction diode. It is a general diode having the same properties and characteristics. 

Some common examples of standard recovery diode are:

1N

1N is a general-purpose silicon rectifier diode. The maximum current carrying capacity of the 1N Diode is 1A, and it can withstand peaks of up to 30A. As a result, we can use it in circuits that use less than 1A. The reverse current is 5uA, which is extremely low. This diode has a power dissipation of 3W.

1N

High-speed switching diodes produced in planar technology and enclosed in hermetically sealed leaded glass SOD27 (DO-35) packages. The maximum current carrying capacity of the IN Diode is 300mA, and it can withstand peaks of up to 2A.

SR360

SR360 is a Schottky Barrier Rectifier with a Low voltage drop of 0.75V and a high forward current of 3A .  This diode offers low power loss, high efficiency, and 80A surge current capability. Low-voltage, high-frequency inverters and polarity protection are some popular uses.

1N

The 1N is a power diode because of its high forward current and high reverse voltage. The maximum current carrying capacity of the 1N Diode is 3A, and it can withstand peaks of up to 200A. As a result, we can use it in circuits that are designed for less than 3A. 

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A fast recovery diode (FRD) is a type of power diode that has a short reverse recovery time for high-frequency rectification. The recovery time is the finite amount of time taken by a diode to discharge (during conducting state, it stored the charges) when switching from the conducting to the blocking state. They are designed to handle high voltage and high current levels than the conventional diode. 

Fast recovery diode consists of two terminals - anode & cathode, and functions the same as that of a conventional diode, but differs in construction. The major construction difference is the presence of the recombination centers in the fast recovery diode. A conventional PN junction diode is formed by joining n-type and p-type semiconductor materials. Whereas in the fast recovery diode, Gold (Au) is added as a dopant to the Gallium Arsenide (GaAs) semiconductor.  This leads to an increment of the number of recombination centers in the forbidden band, which results in a reduction of reverse recovery time at the instant of switching. This construction difference ensures the fast recovery diode exhibit a very small reverse recovery time than a normal diode.

Fast recovery diodes are ideal for use in applications such as switching power supplies, DC-DC converters, AC-DC adaptors/chargers, inverters, motor control & drives, power converter & inverter for wind turbines, commercial, construction & agricultural vehicles (CAV), UPS, and PFC.

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