Characteristics and parameters of high frequency rectifier diode

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Characteristics and parameters of high frequency rectifier diode

The rectifier diodes in the switching power supply must have the characteristics of forward voltage reduction and fast recovery, as well as sufficient output power. The following three types of rectifier diodes can be used: fast recovery rectifier diodes; ultra fast recovery rectifier diodes; Schottky rectifier diodes. The fast recovery and Super Fast Recovery Rectifiers have moderate and high forward voltage drop, which range from 0.8 to 1.2V. These two rectifiers also have high cut-off voltage parameters. Therefore, they are especially suitable for use in the auxiliary power circuit with small power and output voltage of about 12V.

Because the working frequency of modern switching power supply is above 20kHz, the reverse recovery time of fast recovery rectifier diode and super fast recovery rectifier diode is reduced to nanosecond level compared with general rectifier diode, so the efficiency of power supply is greatly improved. According to experience, when choosing fast recovery rectifier diode, its reverse recovery time should be at least 1 / 3 of the rise time of switching transistor. These two rectifiers also reduce the switching voltage spike, which directly affects the ripple of the output DC voltage. In addition, although some called soft recovery rectifier diodes have less noise, their reverse recovery time is longer, and the reverse current is larger, so the switching loss increases, which can not meet the requirements of switching power supply.

Whether the fast recovery rectifier diode and super fast recovery rectifier diode need a radiator when they are used as rectifiers in switching power supply depends on the maximum power of the circuit. Generally, the junction temperature of these diodes is allowed to be 175 ℃, and the manufacturer has technical specifications for this index, so as to provide the designer with the calculation of the maximum output working current, voltage and shell temperature Even under the action of large forward current, the forward voltage drop of Schottky rectifier diode is very low, only about 0.4V. Moreover, with the increase of junction temperature, the forward voltage drop is lower. Therefore, Schottky rectifier diode is particularly suitable for low-voltage output circuit of about 5V. The reverse recovery time of Schottky rectifier diode can be ignored, because this device is a majority of carrier semiconductor devices, in the switching process of the device, there is no problem of clearing a few carrier storage charges.

Schottky rectifier diodes have two disadvantages: first, the reverse cut-off voltage is low, and the current product is about 100V; second, the reverse leakage current is large, which makes the device more vulnerable to thermal breakdown than other types of rectifier devices. Of course, these shortcomings can also be overcome by increasing the instantaneous over-voltage protection circuit and properly controlling the junction temperature. The characteristics and parameters of typical high-speed rectifiers are shown.