Special diodes

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Special diodes

1. Zener diode 　　Zener diode, also known as voltage regulator diode, is a special type of surface contact silicon crystal diode. Because it can stabilize voltage, it is often used in voltage stabilization equipment and some electronic circuits. 　　 　　 　　The characteristic curve of the voltage regulator diode is basically similar to that of an ordinary diode, except that the reverse characteristic curve of the voltage regulator diode is steeper.　　　　 　　The normal working range of the voltage regulator diode is the A and B sections where the reverse current on the volt-ampere characteristic curve begins to rise suddenly. The current in this section is generally a few milliamperes to tens of milliamperes for commonly used low-power voltage regulator tubes. 　　　　　　　　　　　　　　　　　　 1. Main parameters of Zener diode 　　(1) Stable voltage Vz 　　The stable voltage is the voltage value across the Zener diode when it is working normally. This value changes slightly with the working current and temperature. Even for the same type of Zener diode, the stable voltage value has a certain dispersion. For example, the stable voltage of 2CW14 silicon Zener diode is 6~7.5V. 　　(2) Dissipated power PM When 　　the reverse current passes through the PN junction of the Zener diode, a certain power loss will be generated and the temperature of the PN junction will also increase. The dissipated power of the tube is determined according to the allowable PN junction operating temperature. Usually, the low-power tube is about a few hundred milliwatts to a few watts. (3) Stable current I Z , minimum stable current I Zmin , maximum stable current I Zmax　　Stable current: the reverse current when the working voltage is equal to the stable voltage; 　　minimum stable current: the minimum reverse current required when the Zener diode works at the stable voltage; 　　maximum stable current: the maximum reverse current allowed to pass through the Zener diode. 　　 2. Application of Zener Diode　　　　　　　　　　 　　Zener diodes are often used after rectification and filtering circuits in small power supply devices to stabilize the DC output voltage. 　　　　　 　　As shown in the figure, the voltage regulator circuit is composed of R and D z . The principle of the voltage regulator tube stabilizing the voltage in the circuit is as follows: 　　　　　 　　As long as the R parameter is properly selected, the increase in Vi can be basically offset, so that Vo remains basically unchanged. 　　It can be seen that in this voltage stabilizing circuit, the main function of automatic regulation is the voltage stabilizing diode Dz . When the output voltage changes slightly, it will cause a large change in the voltage stabilizing diode current Iz . Through the compensation effect of the current limiting resistor R, the output voltage Vo is kept basically unchanged. Selection of current limiting resistor R: 　　1. When I 0 = I 0min and VI = VImax , the requirements are: 　　　　 　　2. When I 0 = I 0max , VI = V Imin , requirements: 　　　　 Therefore, the value range of R is: