How to select fast recovery diodes in circuit applications

How to select fast recovery diodes in circuit applications

When using fast recovery diodes in circuit applications, how should the diode model be selected and what parameters should be considered?

1. Average rectification current IF: Refers to the average forward current that a diode is allowed to pass through during long-term operation. The current is determined by the junction area and heat dissipation conditions of the PN junction. When using, it should be noted that the average current passing through the diode should not exceed this value and meet the heat dissipation conditions. For example, the IF of the 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 destroyed, leading to 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 1OOOV

3. Reverse current IR: It is the reverse current allowed to flow through the diode at the highest reverse operating voltage, and this parameter reflects the unidirectional conductivity of the diode. 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 reverse is a soft characteristic, it refers to the voltage value under a given reverse leakage current condition.

5. Operating frequency fm: It is the highest operating frequency of the diode under normal conditions. 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 diodes 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 capacitor CO: refers to the sum of the diffusion capacitance and junction capacitance when the voltage at both ends of the diode is zero. It is worth noting that due to manufacturing process limitations, even the same model of diode has significant parameter dispersion. The parameters given in the manual are often within a range. If the testing conditions change, the corresponding parameters will also change. For example, the IR of the 1N5200 series silicon encapsulated rectifier diode measured at 25 ° C is less than 1OuA, while the IR becomes less than 500uA at 100 ° C.

When selecting and purchasing fast recovery diodes, their performance needs to be tested. The specific methods are as follows

100% with a multimeter × R or 1000 × Measure the two outgoing lines of the rectifier diode in the R ohm range (with the head and tail swapped once each). If the resistance values measured twice differ significantly, such as those with high resistance values reaching several hundred thousand Ω and those with low resistance values being only a few hundred Ω or even smaller, it indicates that the diode is good (except for those with soft breakdown). If the resistance values measured twice are almost equal and the resistance values are very small, it indicates that the diode has been broken down and cannot be used.