How a Zener diode differs from a normal diode

The parameters, principles and functions of the Zener diode are different from those of ordinary diodes.

The parameters are different

Diode dynamic resistance, the ratio of the change in voltage near the quiescent operating point Q of the diode characteristic curve to the change in the corresponding current.

The dynamic resistance of the regulator diode refers to the ratio of the voltage change at both ends of the regulator diodee to the current change. This ratio varies with the operating current, generally the higher the operating current, the smaller the dynamic resistance. For example, when the operating current of the 2CW7C regulator is 5mA, the Rz is 18Ω; When the operating current is 1OmA, the Rz is 8Ω; At 20mA, Rz is 2Ω; > 20mA is basically the same value.

The principle is not the same

The crystal diode is a p-n junction formed by a p-type semiconductor and an n-type semiconductor, which forms a space charge layer on both sides of its interface and has a self-built electric field. In the absence of an applied voltage, the diffusion current caused by the difference in carrier concentration on both sides of the PN junction and the drift current caused by the self-generated electric field are equal.

When there is a forward voltage bias in the external area, the mutual suppression effect of the external electric field and the self-built electric field increases the diffusion current of the carriers, resulting in the forward current. When there is a reverse voltage bias in the outside world, the external electric field and the self-built electric field are further strengthened to form a reverse saturation current I0 that is independent of the reverse bias voltage value within a certain reverse voltage range.

The reverse characteristic of the Zener diode is that when the reverse voltage is lower than the reverse breakdown voltage, the reverse resistance is very large, and the reverse leakage current is very small. However, when the reverse voltage approaches the critical value of the reverse voltage, the reverse current increases abruptly, called a breakdown, at which the reverse resistance suddenly drops to a very small value. Although the current varies over a wide range, the voltage across the diode is basically stable around the breakdown voltage, enabling the diode to be regulated.

The role is not the same

The functions of diodes include rectifier circuits, detection circuits, voltage regulator circuits, and various modulation circuits, which are mainly composed of diodes.

Voltage regulator diodes, overvoltage protection circuits in TVs, arc suppression circuits, etc.

For example, the overvoltage protection circuit in the TV, 115V is the main power supply voltage of the TV, when the output voltage of the power supply is too high, D is on, and the transistor T is on, and the collector potential will be changed from the original high level (5V) to low level, and the TV will enter the standby protection state through the voltage of the standby control line.