Characteristics and Applications of Fast Recovery Diodes

Characteristics and Applications of Fast Recovery Diodes

The switching speed of fast recovery diode is much higher than that of common diode and switching diode, and it is commonly used for switching power supply output, switching power supply, charger, high-frequency heating equipment, converter, Ultrasonic cleaning, electric welding machine, UPS, and motor control. A semiconductor device used to convert alternating current into direct current. The most important characteristic of a diode is its unidirectional conductivity. In a circuit, current can only flow in from the positive pole of the diode and out from the negative pole. Usually it contains a PN junction with two terminals, positive and negative.

The charge carriers in the P region are holes, while the charge carriers in the N region are electrons, forming certain potential barriers in the P and N regions. When an external voltage causes the P region to have a positive voltage relative to the N region, the barrier decreases, and storage carriers are generated near both sides of the barrier. They can pass through large currents and have a low voltage drop (typical value is 0.7V), which is called a forward conduction state. If the opposite voltage is applied, the barrier increases and can withstand a high reverse voltage, passing a small reverse current (called reverse leakage current), which is called a reverse blocking state. The rectifier diode has obvious unidirectional conductivity. Rectifier diodes can be made of materials such as semiconductor germanium or silicon.

The silicon rectifier diode has high breakdown voltage, low reverse leakage current, and good high-temperature performance. Usually, high-voltage high-power rectifier diodes are made of high-purity monocrystalline silicon (which is prone to reverse breakdown when heavily doped). This type of device has a large junction area and can pass a large current (up to thousands of amperes), but its operating frequency is not high, usually below tens of kilohertz. Rectifier diodes are mainly used in various low-frequency half wave rectification circuits. To achieve full wave rectification, they need to be connected into a rectifier bridge for use.

Fast recovery rectifier diodes belong to the high-frequency rectifier diodes in rectifier diodes, and are called Fast Recovery Diodes because ordinary rectifier diodes generally operate at low frequencies (such as 50Hz mains frequency), with a working frequency below 3kHz. When the working frequency is in the tens to hundreds of kHz, the time of forward and reverse voltage changes is slower than the recovery time, and ordinary rectifier diodes cannot achieve one-way conduction normally, At this point, a fast recovery rectifier diode needs to be used.

The characteristic of a fast recovery diode is its short recovery time, which makes it suitable for high-frequency (such as line frequency in television) rectification. The fast recovery diode has an important parameter that determines its performance - reverse recovery time. The definition of reverse recovery time is the time required for a diode to rapidly transition from a forward conduction state to a cut-off state, from the output pulse dropping to the zero line, to the reverse power source recovering to 10% of the maximum reverse current, commonly represented by the symbol trr. The TRR of ordinary fast recovery rectifier diodes is several hundred nanoseconds (10-9s), while the TRR of ultra Fast Recovery Diodes is generally several tens of nanoseconds. The smaller the Trr, the higher the operating frequency of the fast recovery diode.