### When the fast recovery diode is applied in the circuit, how to select the diode model and what param

1. Average rectifier current IF: refers to the average forward current that the diode is allowed to pass during long-term operation. The current is determined by the junction area and heat dissipation conditions of the PN junction. During use, it should be noted that the average current through the diode should not be greater than this value, and the heat dissipation conditions should be met. For example, the IF of 1N4000 series diode is 1A.

2. Reverse working voltage VR: refers to the maximum reverse voltage allowed to be applied at both ends of 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 damaged, resulting in reverse breakdown. Generally, half of the reverse breakdown voltage (VB) is taken as (VR). For example, 1N4001's VR is 50V, 1N4007's VR is 1OOOV

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 unidirectional conductivity of the diode. Therefore, the smaller the current value, the better the diode quality.

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 soft, it refers to the voltage value under the given reverse leakage current condition.

5. Working frequency fm: It is the highest working 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 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 diffusion capacitance and junction capacitance when the voltage at both ends of the diode is zero. It is worth noting that due to the limitation of manufacturing process, even the same type of diode has a large dispersion of its parameters. The parameters given in the manual are often a range. If the test conditions change, the corresponding parameters will also change. For example, the IR of 1N5200 series silicon molded rectifier diode measured at 25 ° C is less than 1OuA, while the IR becomes less than 500uA at 100 ° C.

The performance of fast recovery diode needs to be tested when selecting and purchasing, and the specific methods are as follows

Use 100% of the multimeter × R or 1000 × R ohm gear, measure the two outgoing lines of the rectifier diode (the head and tail are adjusted for one time respectively). If the resistance values measured two times differ greatly, for example, the resistance value is as high as several hundred thousand Ω, while the resistance value is only a few hundred Ω or even less, it indicates that the diode is good (except for the diode with soft breakdown). If the resistance values measured twice are almost equal and the resistance value is very small, it indicates that the diode has been broken down and cannot be used.

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