Notes on the use of Zener diodes

Notes on the use of Zener diodes:

1, should pay attention to the difference between the general diode and the Zener diode. A lot of general diodes, especially glass-encapsulated tubes, have similar color shapes and similarities to Zener diodes. If you don't carefully distinguish them, you will use them incorrectly. The difference is: look at the shape, a lot of Zener diodes are cylindrical, short and thick, and the general diode is slender if it is cylindrical; look at the sign, the outer surface of the Zener diode is marked with voltage regulator Value, such as 5V6, indicates that the voltage regulation value is 5.6V; use a multimeter to measure, according to the unidirectional conductivity, use the X1K block to judge the positive and negative polarity of the diode to be tested first, then use X10K block, black pen to connect the diode negative The red pen is connected to the positive pole of the diode. The measured resistance value is larger than that of the X1K gear. If the reverse resistance value is large, the possibility of a general diode is very large. If the reverse resistance value becomes small, then It is a Zener diode.

2. Pay attention to the difference between forward and reverse use of Zener diodes. When the Zener diode is used in forward conduction, it is basically the same as the normal diode forward conduction. The voltage at both ends after the forward conduction is basically constant, and is about 0.7V. In theory, the Zener diode can also be used as a Zener diode in the forward direction, but its voltage regulation value will be lower than 1V, and the voltage regulation performance is not good. Generally, the forward conduction characteristic of the Zener diode is not used alone to stabilize. Pressure, but with reverse breakdown characteristics to regulate. The reverse breakdown voltage value is the regulation value. Sometimes two Zener diodes are used in series, one uses its forward characteristic, and the other uses its reverse characteristic to both regulate and temperature compensate to improve the voltage regulation.

3, should pay attention to the role of the current limiting resistor and the impact of the magnitude of the resistance. In the Zener diode voltage regulator circuit, a resistor R is generally connected in series, as shown in Figure 1 or 2. This resistor acts as a current limiter in the circuit and improves the voltage regulation effect. If the resistance is not applied, when R=0, it is easy to burn out the Zener tube, and the voltage regulation effect will be extremely poor. The larger the resistance of the current limiting resistor, the better the voltage regulation performance of the circuit, but the input and output voltage difference will be too large, and the power consumption will be more.

4, pay attention to the pressure difference between input and output. In normal use, the output voltage of the Zener diode voltage regulator circuit is equal to the voltage regulation value at both ends of the Zener diode after reverse breakdown. If the voltage value input to the voltage regulator circuit is less than the voltage regulator voltage, the circuit will Loss of voltage regulation, only when it is greater than the relationship, there is a voltage regulation effect, and the larger the voltage difference, the larger the resistance value of the current limiting resistor should be, otherwise the voltage regulator tube will be damaged.

5, the voltage regulator can be used in series. After several series of voltage regulators are connected in series, a plurality of different voltage regulation values can be obtained, so that series connection is more common. The following example shows how to obtain the voltage regulation value after the two voltage regulators are used in series. If the voltage regulation value of a Zener diode is 5.6V, the other voltage regulation value is 3.6V, and the voltage of the Zener voltage regulator is 0.7V, there are four different voltage regulation values after the series connection.

6, the regulator tube is generally not used in parallel. After several Zener diodes are connected in parallel, the regulation value will be determined by the lowest one (including the voltage value after forward conduction). Take the above two voltage regulators as an example to illustrate the calculation method of the voltage regulation value. There are four cases after the two parallel connections, and the voltage regulation value is only two. Zener diodes are not used in parallel unless otherwise specified.