Characteristics and common parameters of rectifier diodes

Rectifier diodes are generally planar silicon diodes, which are used in various power rectifier circuits. When selecting a rectifier diode, the parameters such as its maximum rectifier current, maximum reverse working current, cut-off frequency and reverse recovery time should be mainly considered.

The rectifier diode used in the ordinary series stabilized power supply circuit does not have high requirements for the reverse recovery time of the cut-off frequency. As long as the rectifier diode with the maximum rectification current and the maximum reverse working current meet the requirements of the circuit is selected. For example, 1N series, 2CZ series, RLR series, etc.

The rectifier diodes used in the rectifier circuit and pulse rectifier circuit of the switching stabilized power supply should be selected with higher operating frequency and shorter reverse recovery time (such as RU series, EU series, V series, 1SR series, etc.) or choose Fast recovery diode. There is also a Schottky rectifier diode. The rectifier diode uses the unidirectional conductivity of the PN junction to convert alternating current into pulsating direct current. The leakage current of the rectifier diode is relatively large, and most of the diodes are packaged with surface contact materials. The appearance of the rectifier diode is shown in Figure 3. In addition, the parameters of the rectifier diode include the maximum rectifier current, which refers to the maximum current value allowed by the rectifier diode for long-term operation. It is the main parameter of the rectifier diode and the main basis for the option of the rectifier diode.

(1) Maximum average rectified current IF: refers to the maximum forward average current allowed to pass through the diode during long-term operation. The current is determined by the junction area of the PN junction and the heat dissipation conditions. It should be noted that the average current through the diode cannot be greater than this value, and the heat dissipation conditions should be met. For example, the IF of the 1N4000 series diode is 1A.

(2) Maximum 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) increases sharply and the unidirectional conductivity of the diode is destroyed, causing reverse breakdown. Usually take half of the reverse breakdown voltage (VB) as (VR). For example, the VR of 1N4001 is 50V, 1N4002-1n4006 are 100V, 200V, 400V, 600V, and 800V, respectively, and the VR of 1N4007 is 1000V.

(3) Maximum reverse current IR: It is the reverse current allowed to flow through the diode under the highest reverse working voltage. This parameter reflects the quality of the unidirectional conductivity of the diode. Therefore, the smaller the current value, the better the diode quality.

(4) Breakdown voltage VB: refers to the voltage value at the sharp bend 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 a given reverse leakage current condition.

(5) Maximum 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 the 1N4000 series diode is 3kHz. In addition, fast recovery diodes are used in the rectification of higher frequency alternating currents, such as switching power supplies.

(6) Reverse recovery time trr: 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 capacitance of the diffusion capacitance and the 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 same type of diode has a large dispersion of its parameters. The parameters given in the manual are often within a range. If the test conditions change, the corresponding parameters will also change. For example, the IR of the 1N5200 series silicon plastic rectifier diode measured at 25°C is less than 10uA, and at 100°C IR becomes less than 500uA.