When the fast recovery diode is applied in the circuit, how should the diode type be selected and what parameters should be considered?

When the fast recovery diode is applied in the circuit, how should the diode type be selected and what parameters should be considered?

1. Average rectified current IF: refers to the forward average current that the diode is allowed to pass through for a long time. This current is determined by the junction area of the PN junction and heat dissipation conditions. When using, it should be noted that the average current through the diode cannot be greater than this value, and the heat dissipation conditions must be met. For example, the IF of a 1N4000 series diode is 1A.

2. Reverse working voltage VR: refers to the maximum reverse voltage allowed to be applied across the diode. If it is greater than this value, the reverse current (IR) will increase sharply, and the unidirectional conductivity of the diode will be destroyed, causing reverse breakdown. Usually half of the reverse breakdown voltage (VB) is taken as (VR). For example, the VR of 1N4001 is 50V, and the VR of 1N4007 is 1000V

3. Reverse current IR: It is the reverse current that the diode is allowed to flow under the highest reverse working voltage. This parameter reflects the quality of the diode's unidirectional conductivity. Therefore, the smaller the current value, the better the quality of the diode.

4. Breakdown voltage VR: refers to the voltage value at the sharp bending point of the reverse volt-ampere characteristic curve of the diode. When the reverse is a soft characteristic, it refers to the voltage value under the given reverse leakage current condition.

5. Operating frequency fm: It is the highest operating frequency of the diode under normal conditions. It is mainly determined by the junction capacitance and diffusion capacitance of the PN junction. If the operating frequency exceeds fm, the unidirectional conductivity of the diode will not be well reflected. For example, the fm of a 1N4000 series diode is 3kHz.

6. Reverse recovery time tre: refers to the reverse recovery time under the specified load, forward current and maximum reverse transient voltage.

7. Zero bias capacitance CO: refers to the sum of the diffusion capacitance and junction capacitance when the voltage across the diode is zero. It is worth noting that due to the limitation of the manufacturing process, even the diodes of the same type have great dispersion in their parameters. The parameters given in the manual are often in a range. If the test conditions change, the corresponding parameters will also change. For example, the IR of the 1N5200 series silicon plastic rectifier diodes measured at 25°C is less than 1OuA, and at 100°C IR becomes less than 500uA.

It is necessary to test the performance of fast recovery diode when selecting and purchasing them. The specific method is as follows

Use the 100×R or 1000×R ohm range of the multimeter to measure the two lead wires of the rectifier diode (reverse the head and the tail and measure once). If there is a large difference between the two measured resistance values, for example, the resistance value is as high as hundreds of thousands of Ω, while the resistance value is only a few hundred Ω or even smaller, indicating that the diode is good (a diode with soft breakdown except). If the resistance values measured twice are almost equal, and the resistance value is very small, it means that the diode has been damaged by breakdown and cannot be used.