Use of zener diodes
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1, pay attention to the difference between the general method of diode and zener diode. Many common diodes, especially glass-encapsulated tubes, are similar in appearance color to zener diodes. If they are not carefully differentiated, they will be misused. The difference is: look at the appearance, many zener diodes are cylindrical, short and thick, and the general diode is cylindrical if the cylindrical shape is relatively slender; look at the logo, the voltage regulator diode is marked with the regulator on the external surface Values, such as 5V6, indicate that the voltage regulator is 5.6V. Use a multimeter to measure. According to the unidirectional conductivity, use the X1K block to first determine the positive and negative polarity of the diode under test, and then use X10K to block the black diode. The red lead is connected to the positive diode. If the measured resistance is larger than that of the X1K, if there is a large reverse resistance, it is very likely to be a common diode. If the reverse resistance becomes very small, then It is a Zener diode.
2. Note the difference between forward and reverse use of zener diodes. When the zener diode is used for forward conduction, it is basically the same as when the general diode is used for forward conduction. The voltage at both ends of the forward conduction is also basically constant, and both are about 0.7V. In theory, the zener diode can also be used in the forward direction as a regulator, but its regulation value will be lower than 1V, and its regulation performance is also not good. Generally, it is not stabilized by the forward conduction characteristics of the regulator tube alone. Pressure, but with reverse breakdown characteristics to regulate. The reverse breakdown voltage value is the voltage regulator value. Sometimes two Zener diodes are used in series, one using its forward characteristic and the other using its reverse characteristic, which can both regulate voltage and temperature compensation to increase the voltage regulation effect.
3, pay attention to the role of the current limiting resistor and the impact of the size of the resistance. In a Zener diode regulator circuit, a resistor R is generally connected in series as shown in FIG. 1 or 2. The resistor acts as a current limiter in the circuit and improves the voltage regulation effect. If this resistor is not added, that is when R=0, the regulator tube will burn out easily and the voltage regulation effect will be extremely poor. The greater the value 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 increase.
4, pay attention to the pressure difference between the input and output. In normal use, the output voltage of the zener diode regulator circuit is equal to the voltage regulator at both ends of the regulator reverse breakdown, if the voltage value input to the regulator circuit is less than the regulator voltage regulator value, the circuit will Loss of regulation, only when it is greater than the relationship, there is a voltage regulator, and the greater the pressure difference, the resistance of the current limiting resistor should be greater, otherwise it will damage the regulator.
5, the regulator tube can be used in series. After several Zener diodes are connected in series, several different voltage regulator values can be obtained. Therefore, serial connection is more common. The following is an example of how to obtain the voltage regulator value after using two regulators in series. If the voltage regulator of a regulator is 5.6V and the other regulator is 3.6V, set the voltage of the regulator tube to be 0.7V during forward conduction. There are four different regulator values after the series connection.
6, regulators are generally not used in parallel. After several regulators are connected in parallel, the regulator value will be determined by one of the lowest (including the voltage after the forward conduction). Or use the above two regulators as an example to illustrate how to calculate the regulation value. There are four cases after two parallel connections, and there are only two voltage regulators. Unless otherwise specified, zener diodes are not used in parallel.
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