How exactly do we choose Schottky diodes?

Schottky diodes are often used in switching power supplies, but due to different manufacturers and other reasons, the performance is very different, and we must consider the following parameters when choosing Schottky:

1. Turn-on voltage drop VF: VF is the voltage drop at both ends of the diode when the diode is forward conducted, and the selection of Schottky diodes is to choose diodes with smaller VF as much as possible.

2. Reverse saturation leakage current IR: IR refers to the current flowing through the diode when the reverse voltage is added at both ends of the diode, and the reverse leakage current of the Schottky diode is larger, and the choice of Schottky diode is to choose the diode with smaller IR as much as possible.

3. Rated current IF: refers to the average current value converted according to the allowable temperature rise of the diode during long-term operation.

4. Maximum inrush current IFSM: The excess forward current that is allowed to flow through. It is not a normal current, but an instantaneous current, which is quite large.

5. Maximum reverse peak voltage VRM: Even if there is no reverse current, as long as the reverse voltage is continuously increased, the diode will be damaged sooner or later. This reverse voltage that can be added is not an instantaneous voltage, but a forward and reverse voltage that is repeatedly added. Since the rectifier is added with an alternating voltage, its maximum value is an important factor specified. Maximum Reverse Peak Voltage VRM refers to the maximum reverse voltage that can be added to avoid breakdown.

6. Maximum DC reverse voltage VR: The above maximum reverse peak voltage is the peak voltage that is added repeatedly, and VR is the value when the DC voltage is continuously added. For DC circuits, the maximum DC reverse voltage is important to determine the allowable and upper limits.

7. Maximum operating frequency fM: Due to the presence of junction capacitance of PN junction, when the working frequency exceeds a certain value, its unidirectional conductivity will become worse. Schottky diodes have a high fM value of up to 100 GHz.

8. Reverse recovery time Trr: When the working voltage changes from forward voltage to reverse voltage, the ideal situation for diode operation is that the current energy can be cut off instantaneously. In fact, there is usually a slight delay. The amount that determines the current cut-off delay is the reverse recovery time. Although it directly affects the switching speed of the diode, it does not necessarily mean that this value is small. That is, when the Schottky diode is abruptly reversed from on, the time required for the reverse current to decay from a large amount to close to the IR. This indicator is very important when the high-power switch is working in the high-frequency switching state.