Characteristics and parameters of high-frequency rectifier diode

The rectifier diode in a switching power supply must possess characteristics such as low forward voltage drop and fast recovery, and should also exhibit sufficient output power. The following three types of rectifier diodes can be employed: fast recovery rectifier diode; ultra-fast recovery rectifier diode; Schottky rectifier diode. Fast recovery and ultra-fast recovery rectifier diodes exhibit moderate and high forward voltage drops, ranging from 0.8 to 1.2V. These two types of rectifier diodes also possess high cut-off voltage parameters. Therefore, they are particularly suitable for use in low-power auxiliary power supply circuits with an output voltage around 12V.

Since modern switching power supplies operate at frequencies above 20kHz, compared to general rectifier diodes, the reverse recovery time of fast recovery rectifier diodes and ultra-fast recovery rectifier diodes has been reduced to the nanosecond level, greatly improving the efficiency of the power supply. According to experience, when selecting fast recovery rectifier diodes, their reverse recovery time should be at least 1/3 of the rise time of the switching transistor. These two types of rectifier diodes also reduce switching voltage spikes, which directly affect the ripple of the output DC voltage. In addition, although some so-called soft recovery rectifier diodes have lower noise, their reverse recovery time is longer and the reverse current is larger, resulting in increased switching losses and thus failing to meet the operational requirements of switching power supplies.

Whether fast recovery rectifier diodes and ultrafast recovery rectifier diodes require a heat sink when used as rectifying devices in switching power supplies depends on the maximum power of the circuit. Generally, the allowable junction temperature of these diodes during manufacturing is 175°C, and manufacturers provide technical specifications for this indicator to assist designers in calculating the maximum output operating current, voltage, and case temperature.

Schottky rectifier diodes exhibit a very low forward voltage drop, approximately 0.4V, even under high forward current conditions. Furthermore, as the junction temperature increases, their forward voltage drop decreases even further. This makes Schottky rectifier diodes particularly suitable for low-voltage output circuits around 5V. The reverse recovery time of Schottky rectifier diodes is negligible because these devices are majority carrier semiconductor devices. During the switching process of the device, there is no issue with clearing minority carrier stored charges.

Schottky rectifier diodes have two major drawbacks: firstly, their low tolerance to reverse cut-off voltage, with current products having a voltage of approximately 100V; secondly, their high reverse leakage current, making the device more susceptible to thermal breakdown compared to other types of rectifying devices. Of course, these drawbacks can be overcome by adding transient overvoltage protection circuits and properly controlling junction temperature. The characteristics and parameters of a typical high-speed rectifier diode are shown.