Overvoltage Protection function of Zener Diode

Overvoltage Protection function of Zener Diode.

The Zener diode has the functions of overvoltage and undervoltage protection, which can prevent the load from being in a low voltage state for a long time and finally disconnect the circuit. It uses the breakdown voltage of the Zener diode. Once the power supply voltage VCC exceeds the breakdown voltage of the Zener diode, the Zener tube will turn on. At this point, the contact K is closed, the relay is turned on, and the load R1 is working. When the VCC voltage is too low (does not reach the stable voltage value of the voltage 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 the use of complementary Zener diodes 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 voltage drop of one diode decreases and the voltage drop of the other diode increases, so the main tube voltage drop of the two diodes remains unchanged, which plays the role of temperature compensation.

The reverse current of the Zener diode when it works stably after reverse breakdown is called stable current. The maximum reverse current allowed to pass through the voltage regulator is called the maximum stable current. When using the voltage stabilizer, the working current can not 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 voltage change Uz to current change I is called dynamic resistance. The smaller the dynamic resistance is, the better the voltage stability is. The temperature change of the Zener diode will lead to a slight change in the stable voltage, so the relative change of the voltage at both ends of the tube caused by the temperature change of 1 ℃ is the temperature coefficient. The smaller the temperature coefficient, the better, indicating that the Zener diode is almost not affected by temperature.

Zener diodes are mainly used in constant voltage source, auxiliary power supply and reference power supply circuit. However, it is usually used for level conversion in digital circuits. Used for the protection of overvoltage circuit. A Zener diode is a semiconductor element with high resistance up to the critical reverse breakdown voltage. Zener diodes always work in the reverse breakdown zone of electronic circuits, so they are connected in the opposite way to ordinary diodes. 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.