Zener diode is different from ordinary diode in parameters, principles and functions.
Different parameters
Diode dynamic resistance, diode characteristic curve The ratio of the change of voltage near the static operating point Q to the change of corresponding current.
The dynamic resistance of voltage stabilizing diode refers to the ratio of voltage change and current change at both ends of voltage stabilizing tube. The ratio varies with the working current. Generally, the larger the working current is, the smaller the dynamic resistance is. For example, when the working current of 2CW7C voltage stabilizing tube is 5mA, Rz is 18 Ω; Rz is 8 Ω when the working current is 1 mA; When it is 20mA, Rz is 2 Ω;> 20mA basically maintains this value.
The principle is different
The crystal diode is a pn junction formed by a p-type semiconductor and an n-type semiconductor. A space charge layer is formed on both sides of the interface, and a self built electric field is built. When there is no applied voltage, the diffusion current caused by the carrier concentration difference on both sides of the pn junction is equal to the drift current caused by the self built electric field and is in electric balance.
When there is a positive voltage bias outside, the mutual suppression of the external electric field and the self built electric field makes the carrier diffusion current increase and causes a positive current. When there is reverse voltage bias outside, the external electric field and self built electric field are further strengthened, forming a reverse saturation current I0 that is independent of the reverse bias voltage within a certain reverse voltage range.
The reverse characteristic of zener diode is that when the reverse voltage is lower than the reverse breakdown voltage, the reverse resistance is large and the reverse leakage current is small. However, when the reverse voltage approaches the critical value of the reverse voltage, the reverse current suddenly increases, which is called breakdown. At this critical breakdown point, the reverse resistance suddenly drops to a very small value. Although the current varies in a large range, the voltage at both ends of the diode is basically stable near the breakdown voltage, thus realizing the voltage stabilizing function of the diode.
Different functions
The diode functions as a rectification circuit, a detection circuit, a voltage stabilizing circuit, and various modulation circuits, which are mainly composed of diodes.
Zener diode, overvoltage protection circuit in TV, arc suppression circuit, etc.
For example, in the over-voltage protection circuit of the television, 115V is the main power supply voltage of the television. When the output voltage of the power supply is too high, D is connected, and the triode T is connected. Its collector potential will change from the original high level (5V) to the low level, and the television will enter the standby protection state through the voltage of the standby control line.
