The principle and usage of Zener Diode

To understand the working principle of Zener diodes, you only need to understand the reverse characteristics of diodes. The basic characteristic of all crystal diodes is unidirectional conduction. That is to say, the positive pressure conduction, the reverse pressure can not pass. There is a condition that the reverse pressure does not exceed the reverse pressure value of the tube. So what is the result after exceeding the withstand voltage value? A simple answer is that the pipe burns out. But that's not the whole answer. It is found that as long as the reverse current value is limited (for example, a resistor is connected in series between the tube and the power supply), the tube will not burn out even though it is broken down. It is also found that after the reverse breakdown of the tube, the current changes from large to small, and the voltage decreases only slightly, until it falls to a certain current value before the voltage drops sharply with the decrease of the current. It is by taking advantage of this feature that people make Zener diodes. The key to using a Zener diode is to design its current value.
The characteristic of Zener diode is that after breakdown, the voltage at both ends of the diode remains basically unchanged. In this way, when the regulator is connected to the circuit, if the voltage of the power supply fluctuates or the voltage of each point in the circuit changes due to other reasons, the voltage at both ends of the load will remain basically unchanged.
Working principle of Zener Diode and Application Circuit of Zener Diode.
one。. Principle and characteristics of Zener Diode.
In general, transistors are forward turn-on, reverse cut-off; if the reverse voltage added to the diode exceeds the bearing capacity of the diode, the diode will be broken down. However, there is a kind of diode whose forward characteristic is the same as that of ordinary diodes, while the reverse characteristic is relatively special: when the reverse voltage is applied to a certain extent, although the tube is in a breakdown state, it is not damaged through a large current, and the repeatability of this phenomenon is very good. Conversely, as long as the tube is in a breakdown state, although the electricity flowing through the tube varies greatly, the voltage at both ends of the tube varies very little to stabilize the voltage. This special diode is called a voltage regulator.
How does this circuit stabilize the voltage?
If the grid voltage increases, the output voltage Usr of the rectifier circuit also increases, resulting in an increase in the load voltage Usc. Because the voltage regulator DW is in parallel with the load Rfz, as long as the root of Usc increases a little, the current flowing through the regulator will increase sharply, so that I1 will also increase, and the voltage drop on the current limiting resistor R1 will increase, thus counteracting the increase of Usr and keeping the load voltage Usc basically unchanged. On the contrary, if the grid voltage decreases, resulting in the decrease of Usr and Usc, the current in the voltage stabilizer decreases sharply, which reduces the I1 and the voltage drop on R1, thus offsetting the decline of Usr and keeping the load voltage Usc basically unchanged.