All the crystal diodes, the basic characteristics of one-way conduction. In other words, the positive pressure conduction, reverse pressure barrier. There is a condition here is the reverse pressure does not exceed the reverse voltage tube value. Then what is the result after exceeding the withstand voltage? A simple answer is that the tube is burned. But this is not the answer. This is actually the working principle of Zener diode, then what is the working principle of Zener diode? Let's take a look.

After the test found that some diodes as long as the limit reverse current value (for example, in series between the tube and the power supply resistance), although the tube is not breakdown will be destroyed. But also found that the reverse breakdown of the tube, the current from small to small, the voltage is only a very small drop, has been down to a certain value of the current voltage dropped sharply with the current decline. It is using this feature people have created a Zener diode. The key to using a Zener diode is to design its current value.

The general diode is the forward conduction, the reverse cut-off; plus the reverse voltage on the diode, if more than the capacity of the diode, the diode breakdown breakdown. But there is a kind of diode, its forward characteristic is the same as the ordinary diode, but the reverse characteristic is quite special: When the reverse voltage adds to a certain extent, although the tube presents the breakdown state, pass the larger electric current, but not destroy, and The repeatability of this phenomenon is very good; on the other hand, as long as the tube is in a breakdown state, the electricity flowing through the tube varies a lot and the voltage across the tube changes very little to stabilize. This special diode is called a regulator.

Zener diode commonly used models are: 1N5221B、1N5236B and so on.

The above is the working principle of the Zener diode. In practical applications, if less than the Zener voltage can be selected, the Zener with the lower Zener voltage can be selected and then one or several Si diodes in series can be selected. Pillow ", the steady voltage increased to the required value. This is the use of silicon diodes forward voltage drop of 0.6 to 0.7 volts to regulate the characteristics. Therefore, the diode in the circuit must be connected forward, which is different from the regulator.