How to measure the rectifier diode _ How to use a multimeter to detect the quality of the rectifier diode

A rectifying diode (recTIfierdiode) is a semiconductor device for converting alternating current into direct current. The most important characteristic of a diode is its unidirectional conductivity. In the circuit, current can only flow from the positive pole of the diode and the negative pole flows out. Usually it contains a PN junction with two terminals, positive and negative. Its structure is shown in the figure. The carriers in the P region are holes, and the carriers in the N region are electrons, forming a certain barrier in the P region and the N region. When the applied voltage makes the P region positive with respect to the N region, the barrier is lowered, and carriers are generated near both sides of the barrier, which can pass a large current and have a low voltage drop (typically 0.7V), which is called positive. Wizard status. If the opposite voltage is applied, the barrier is increased to withstand a high reverse voltage, and a small reverse current (called reverse leakage current) is called a reverse blocking state. The rectifier diode has significant unidirectional conductivity. The rectifier diode can be fabricated from materials such as semiconductor germanium or silicon. The silicon rectifier diode has a high breakdown voltage, a small reverse leakage current, and good high temperature performance. Usually high-voltage and high-power rectifier diodes are made of high-purity single crystal silicon (it is easy to reverse breakdown when doping more). This device has a large junction area and can pass a large current (up to thousands of amps), but the operating frequency is not high, generally below several tens of kilohertz. Rectifier diodes are mainly used in various low-frequency half-wave rectification circuits. If full-wave rectification is required, they must be connected to a rectifier bridge.

The rectifier diode uses the unidirectional conduction characteristic of the PN junction to convert the alternating current into a pulsating direct current. The rectifier diode has a large leakage current, and most of the diodes are packaged in a surface contact material. The shape of the rectifier diode is shown in Figure 1. In addition, the parameters of the rectifier diode are the maximum rectified current, which is the maximum current allowed by the rectifier diode for a long time. It is the main parameter of the rectifier diode and is the main basis for the rectifier diode of the option.

(1) Maximum average rectified current IF: refers to the maximum forward average current allowed to pass through the diode for long-term operation. This current is determined by the junction area of ​​the PN junction and the heat dissipation conditions. When using, please pay attention to the average current through the diode can not be greater than this value, and to meet the heat dissipation conditions. For example, the 1N4000 series diode has an IF of 1A.

(2) The highest reverse operating voltage VR: refers to the maximum reverse voltage allowed to be applied across the diode. If it is larger than this value, the reverse current (IR) sharply increases, and the unidirectional conductivity of the diode is broken, causing reverse breakdown. Usually half of the reverse breakdown voltage (VB) is taken as (VR). For example, the VR of the 1N4001 is 50V, the 1N4002-1n4006 is 100V, 200V, 400V, 600V, and 800V, respectively. The VR of the 1N4007 is 1000V.

(3) Maximum reverse current IR: It is the reverse current that the diode is allowed to flow at the highest reverse operating voltage. This parameter reflects the unidirectional conduction performance of the diode. Therefore, the smaller the current value, the better the diode quality.

(4) Breakdown voltage VB: refers to the voltage value at which the diode reverse volt-ampere characteristic curve sharply bends. When the reverse is a soft characteristic, it refers to the voltage value given the 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 the diffusion capacitance of the PN junction. If the operating frequency exceeds fm, the unidirectional conduction performance of the diode will not be well reflected. For example, the 1m4000 series diode has an fm of 3 kHz. Another fast recovery diode is used for rectification of higher frequency AC power, such as in 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 capacitor and the junction capacitor when the voltage across the diode is zero. It is worth noting that due to the limitations of the manufacturing process, even the same type of diode has a large parameter dispersion. 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 the 1N5200 series silicon plastic-sealed rectifier diode is less than 10uA at 25°C, and at 100°C. The IR becomes less than 500 uA.