A zener diode is a single PN junction diode used to stabilize the voltage. This diode is a semiconductor device that has a very high resistance until the critical reverse breakdown voltage. In this article, we mainly discuss the working principle of the Zener.

The crystal diode is a p-n junction formed of a p-type semiconductor and an n-type semiconductor. A space charge layer is formed on both sides of the crystal diode, and a self-built electric field is built. When there is no applied voltage, the diffusion current caused by the difference in carrier concentration on both sides of the p-n junction is equal to the drift current caused by the self-built electric field and is in an electric equilibrium state. When the outside world is biased by the forward voltage, mutual suppression of the external electric field and the self-built electric field increases the diffusion current of the carrier and causes a forward current. When the outside world has a reverse voltage bias, the external electric field and the self-built electric field are further strengthened to form a reverse saturation current I0 independent of the reverse bias voltage value within a certain reverse voltage range. When the applied reverse voltage is high to a certain extent, the electric field intensity in the space charge layer of the pn junction reaches a critical value and the carrier multiplication process is generated, generating a large number of electron-hole pairs, resulting in a large reverse breakdown current This is called the diode breakdown phenomenon.

If the grid voltage increases, the output voltage Usr of the rectifier circuit also increases, causing the load voltage Usc to rise. Since the Zener diode DW is connected in parallel with the load Rfz, as long as there is little root growth in the Usc, the current flowing through the Zener diode will increase drastically, so that I1 will also increase and the voltage drop across the current limiting resistor R1 will increase, thus canceling out. The rise of Usr keeps the load voltage Usc basically unchanged. Conversely, if the grid voltage drops, causing Usr to drop, causing Usc to fall, the current in the Zener diode decreases sharply, which causes I1 to decrease, and the voltage drop across R1 also decreases, thereby canceling the Usr drop, maintaining the load. The voltage Usc remains basically unchanged.

If Usr is constant and the load current increases, the voltage drop across R1 increases, causing the load voltage Usc to drop. As soon as Usc drops a little, the current in the Zener diode decreases rapidly, causing the voltage drop across R1 to decrease again, thereby keeping the voltage drop across R1 essentially constant, allowing the load voltage Usc to stabilize.

The above is the working principle of the zener diode.