Characteristics and application of fast recovery diode

Characteristics and application of fast recovery diode

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

The carriers in the P region are holes, and the carriers in the N region are electrons, forming a certain potential barrier between the P region and the N region. When the applied voltage makes the P-region positive relative to the N-region, the potential barrier is lowered, and stored carriers are generated near both sides of the potential barrier, which can pass a large current and has a low voltage drop (typically 0.7V), which is called a forward conduction state. If the opposite voltage is applied, the potential barrier is increased, and it can withstand a high reverse voltage, and a small reverse current (called reverse leakage current) flows, which is called reverse blocking state. The rectifier diode has obvious unilateral conductivity. The rectifier diode can be made of semiconductor germanium or silicon.

Silicon rectifier diode has high breakdown voltage, low reverse leakage current and good high temperature performance. Usually, high-voltage and high-power rectifier diodes are made of high-purity monocrystalline silicon (it is easy to reverse breakdown when doped too much). This device has a large junction area and can pass a large current (up to thousands of amperes), but its working frequency is not high, generally below tens of kilohertz. Rectifier diodes are mainly used in various low-frequency half-wave rectifier circuits. If full-wave rectification is needed, they need to be connected as a rectifier bridge.

Fast recovery rectifier diode belongs to the high-frequency rectifier diode, so it is called fast recovery diode, because ordinary rectifier diode generally works at low frequency (for example, the commercial frequency is 50Hz), and its working frequency is lower than 3kHz. When the working frequency is tens to hundreds of kHz, the time of forward and backward voltage changes is slower than the recovery time, so ordinary rectifier diode can't realize unidirectional conduction normally, so it is necessary to use fast recovery rectifier diode.

The characteristic of fast recovery diode is its short recovery time, which makes it suitable for high frequency (such as line frequency in TV) rectification. Fast recovery diode has an important parameter that determines its performance-reverse recovery time. The reverse recovery time is defined as the time required for the diode to switch sharply from the forward conduction state to the off state, from the time when the output pulse drops to the zero line, to the time when the reverse power supply recovers to 10% of the maximum reverse current, which is usually represented by the symbol trr. The trr of common fast recovery rectifier diode is several hundred nanoseconds (10-9s), while that of ultra-fast recovery diode is generally several tens of nanoseconds. The smaller the Trr, the higher the operating frequency of the fast recovery diode.