China Rectifier Diode Supplier

What is a rectifier diode?
A semiconductor device that converts AC power into DC power. Usually it consists of a PN junction with two terminals, positive and negative. The most important characteristic of a diode is unidirectional conductivity. In the circuit, current can only flow in from the positive terminal of the diode and flow out from the negative terminal.

Introduction of rectifier diode

A rectifier diode is a semiconductor device used to convert alternating current to direct current. The most important characteristic of a diode is unidirectional conductivity. In the circuit, current can only flow in from the positive terminal of the diode and flow out from the negative terminal. Usually it consists of a PN junction with two terminals, positive and negative. Its structure is shown in Figure 2. The carriers in the P region are holes, and the carriers in the N region are electrons, forming a certain potential barrier between the P region and the N region. When the applied voltage makes the P region a positive voltage relative to the N region, the potential barrier is lowered, and storage carriers are generated near both sides of the potential barrier, which can pass a large current and have a low voltage drop (typically 0.7V), which is called positive to the ON state. If the opposite voltage is applied, the potential barrier is increased, it can withstand high reverse voltage, and a small reverse current (called reverse leakage current) flows, which is called reverse blocking state. Rectifier diodes have obvious unidirectional conductivity. Rectifier diodes can be made of materials such as semiconductor germanium or silicon. Silicon rectifier diodes have high breakdown voltage, low 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 doped more). This kind of 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 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 into a rectifier bridge.

Characteristics of Rectifier Diodes

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 large, and most of them are packaged with surface-contact materials. The shape of the rectifier diode is shown in Figure 3. In addition, in addition to the parameters of the rectifier diode, there is also a maximum rectification current, which refers to the maximum current value that the rectifier diode allows to pass through for a long time. It is the main parameter of the rectifier diode and the main basis for the optional rectifier diode.

Common parameters of rectifier diodes

(1) Maximum average rectified current IF: Refers to the maximum forward average current allowed to pass through the diode when it works 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, a 1N4000 series diode has an IF of 1A.
(2) The highest 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, 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 that the diode allows 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 VB: 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) Maximum operating frequency fm: It is the highest operating frequency of the diode under normal conditions, and 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, a 1N4000 series diode has an fm of 3kHz. Another fast recovery diode is used for the rectification of high frequency alternating current, such as switching power supply.

(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: It 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 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 10uA, while at 100°C the IR becomes less than 500uA.

Causes of damage to rectifier diodes

(1) Lightning protection and overvoltage protection measures are weak. The rectifier is not equipped with lightning protection and overvoltage protection devices. Even if lightning protection and overvoltage protection devices are installed, their work is unreliable, and the rectifier tube will be damaged due to lightning strike or overvoltage.
(2) The operating conditions are bad. For generator sets with indirect transmission, because the calculation of the speed ratio is incorrect or the ratio of the diameters of the two belt pulleys does not meet the requirements of the speed ratio, the generator runs at high speed for a long time. The rectifier also works at a higher voltage for a long time, which accelerates the aging of the rectifier and is prematurely broken down and damaged.
(3) Poor operation management. The operating personnel on duty are irresponsible and do not understand the change of external load (especially between 0:00 in the middle of the night and 6:00 in the morning of the next day), or when a load shedding failure occurs in the outside world. The operating personnel did not carry out the corresponding operation and treatment in time, resulting in overvoltage and breakdown and damage to the rectifier tube.
(4) Equipment installation or manufacturing quality is not up to standard. Since the generator set has been operating in a large vibration for a long time, the rectifier is also under the external force interference of this vibration; At the same time, due to the high and low speed of the generator set, the working voltage of the rectifier tube also varies from high to low, which greatly accelerates the aging and damage of the rectifier tube.
(5) The specifications and models of the rectifier tubes do not match. When replacing a new rectifier tube, the rectifier diode whose working parameters do not meet the requirements is wrongly replaced or the wiring is wrong, resulting in breakdown and damage to the rectifier tube.
(6) The safety margin of the rectifier tube is too small. The overvoltage and overcurrent safety margins of the rectifier are relatively small, so that the rectifier cannot withstand the attack of the overvoltage or the peak value of the overcurrent transient process that occurs in the excitation circuit of the generator and is damaged.

Replacement of rectifier diodes

After the rectifier diode is damaged, it can be replaced with a rectifier diode of the same type or another type of rectifier diode with the same parameters.
Generally, a rectifier diode with a high withstand voltage (reverse voltage) can replace a rectifier diode with a low withstand voltage, while a rectifier diode with a low withstand voltage cannot replace a rectifier diode with a high withstand voltage.

Inspection method of rectifier diode

First remove all the rectifier diodes in the rectifier, and use the 100×R or 1000×R ohm range of the multimeter to measure the two lead wires of the rectifier diodes (reverse the head and tail and measure once). If there is a big difference between the two measured resistance values, for example, the large resistance value is as high as hundreds of KΩ to infinity, while the small resistance value is only a few hundred Ω or even smaller, indicating that the diode is good. 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. If the resistance value of the two measurements is infinite, it means that the diode has been disconnected internally and cannot be used.