The Zener diode has over-voltage and under-voltage protection functions, which can prevent the load from being in a low voltage state for a long time and eventually disconnect the circuit. It uses the breakdown voltage of a Zener diode. Once the power supply voltage VCC exceeds the breakdown voltage of the Zener diode, the Zener diode will be turned on. At this time, the contact K is closed, the relay is turned on, and the load R1 works. When the VCC voltage is too low (not reaching the stable voltage value of the regulator), the contact does not work and the relay will not close.
The Zener diode uses the temperature coefficient of the Zener diode in the temperature compensation circuit. In circuits where a complementary zener diode requires higher voltage stability, especially the effect of temperature on voltage, there are actually two common zener diodes in this temperature complementary zener diode. However, their temperature characteristics are opposite. When the temperature rises or falls, the tube voltage drop of one diode decreases, and the tube voltage drop of the other diode increases, so the total tube voltage drop of the two diodes remains unchanged, which plays a role of temperature compensation.
The reverse current when the Zener diode works stably after reverse breakdown is called the stable current. The maximum reverse current allowed through the voltage regulator tube is called the maximum stable current. When using a Zener tube, the working current cannot exceed, and it is generally designed to be more than 2 times the output voltage. When the Zener diode works on the reverse breakdown curve, the ratio of the voltage change △Uz to the current change △I is called dynamic resistance. The smaller the dynamic resistance, the better the voltage regulation performance. The temperature change of the Zener diode will cause a slight change in the stable voltage, so the relative change in the voltage across the tube caused by the 1°C temperature change is the temperature coefficient. The smaller the temperature coefficient, the better, indicating that the Qi Zener diode is hardly affected by temperature.
Zener diodes are mainly used for constant voltage sources, auxiliary power supplies and reference power circuits. However, it is usually used for level conversion in digital circuits. Used for protection of overvoltage circuits. Zener diode is a semiconductor element with high resistance up to the critical reverse breakdown voltage. The Zener diode always works in the reverse breakdown zone of the electronic circuit, so its connection method is just the opposite of that of the ordinary diode. The selected Zener diode should meet the requirements of the main parameters in the application circuit. The stable voltage value of the Zener diode should be the same as the reference voltage value of the application circuit, and the maximum stable current of the Zener diode should be about 50% higher than the maximum load current of the application circuit.
The above explained is the overvoltage protection function of Zener diodes. I hope it will be helpful to you after reading it. If you want to know more about Zener diodes, please contact customer service online or call our company's service Hotline (upper right corner of the website) for consultation, we will be happy to provide you with quality service!