Summary and Analysis of Several Voltage Stabilizer Circuits Power Supply Circuit Zener Diode Voltage Stabilizer The function of the voltage stabilizer circuit is to stabilize the output voltage of the power supply circuit. Due to various reasons, the supply voltage of the AC grid is often unstable, so the DC voltage output by the rectifier and filter circuit will also be unstable. On the other hand, since the rectifier filter circuit must have internal resistance, when the load current changes, the output voltage will also be affected and changed. In order to obtain a stable DC voltage, a voltage regulator circuit must be used after the rectifier filter circuit.

1. What is a Zener Diode

1. Introduction of voltage regulator tube

A kind of Zener diode, it is special, the basic structure is the same as that of ordinary diodes, and it also has a PN junction. Due to different manufacturing processes, when the PN junction is in a reverse breakdown state, the PN junction will not be damaged (the PN junction of ordinary diodes will be damaged). Breakdown characteristics. Generally, when the reverse voltage of the diode exceeds its reverse withstand voltage value, it will be broken down and damaged, but when the zener diode withstands the reverse voltage and reaches the regulated value, the reverse current increases sharply. As long as the reverse current value does not exceed the maximum allowable current, it can work normally, and its reverse volt-ampere characteristic curve is steep and linear.

2. The working principle of the voltage regulator tube

The following figure is the volt-ampere characteristic curve of the Zener diode. When the voltage reaches the voltage regulator value Uz, the curve is very steep, indicating that when the current flowing through the Zener diode changes in size, the voltage across the Zener diode is basically unchanged. That is to say, within a certain voltage range, as the current flowing through the Zener diode changes, the voltage across the Zener diode remains basically unchanged. This is the working principle of the Zener diode, which uses its reverse working characteristics.

2. Application of Zener Diode

Zener diodes are widely used in regulated power supplies, electronic igniters, DC level shifting, limiting circuits, overvoltage protection circuits, compensation circuits, etc.

1. Voltage stabilizer circuit

2. Overvoltage protection

3. Temperature compensation

4. Limiter circuit

Three, different types of voltage regulator circuits

1. Simple voltage regulator circuit

In the reverse breakdown state of the semiconductor Zener diode, although the current changes in a large range, the voltage across its two ends is basically unchanged. Using this characteristic of the Zener diode, a simple voltage regulator circuit can be formed. The circuit is shown in the figure, the Zener diode VD is connected in parallel with the load resistor RL, the voltage on VD is the output voltage U0, and R1 is the current limiting resistor. The Zener diode works in the reverse breakdown state, and its reverse breakdown voltage is the stable voltage U2, as shown in the volt-ampere characteristic curve in Figure 5-85. At UZ, when the current changes in a large range, the voltage basically does not change. Change.
Simple voltage regulator circuit diagram

The simple adjustable voltage stabilizer power supply adopts three-terminal adjustable voltage stabilizer integrated circuit LM317 , so that the voltage adjustable range is 1.5~25V, and the maximum load current is 1.5A.

The working principle of the circuit: After the 220V alternating current is stepped down by the transformer T, the 24V alternating current is obtained; then the full-bridge rectification composed of VD1~VD4 and C1 filtering are used to obtain a DC voltage of about 33V. The voltage is regulated output after the integrated circuit LM317. By adjusting the potentiometer RP, the output voltage can be adjusted continuously. In the figure, C2 is used to eliminate parasitic oscillation, C3 is used to suppress ripple, and C4 is used to improve the transient response of the regulated power supply. VD5 and VD6 play a protective role when the output capacitor leaks or the adjustment terminal is short-circuited. The LED is the working indicator of the regulated power supply, and the resistor R1 is the current limiting resistor. A miniature voltmeter PV is installed at the output end, which can visually indicate the output voltage value.

Simple Zener Voltage Regulator Circuit

It consists of a current limiting resistor R1 and a voltage regulator tube D1. Ui is the input voltage; Uo is the output voltage, that is, the voltage Vz across the Zener tube (the circuit is in parallel). The circuit in this example can be used as a reference voltage source, and can also be used alone as a voltage regulator circuit with a fixed output voltage and a small load current, which has strong practicability.

Its voltage regulation principle is as follows:

When the load resistance remains unchanged and the input voltage Ui increases (or the input voltage remains unchanged, the load resistance RL increases), the output voltage Uo will rise, so that the reverse voltage of the Zener tube D1 will increase slightly, and then flow through the stable The current of the pressure tube D1 increases, so the current flowing through the resistor R1 will increase, and the voltage drop on the current limiting resistor R1 will become larger, so that most of the voltage drop of the Ui increment is consumed on R1, so that the output voltage Uo is basically stay the same.

Conversely, when the load resistance remains unchanged and the input voltage Ui decreases (or the input voltage remains unchanged and the load resistance RL decreases), the output voltage Uo will drop, so that the reverse voltage of the Zener tube D1 will also drop, and the flow through the stable The reverse current of the pressure tube D1 also drops slightly, so the current flowing through the resistor R1 will decrease, and the voltage drop across the current limiting resistor R1 will become smaller, so the voltage of Uo will rise again, so after stabilization, the voltage Uo is still basically stay the same.

Summary: Whether the amount of change increases or decreases. All will cause changes in the voltage drop of the current limiting resistor R, thereby maintaining the stability of the output.

2. Series voltage regulator circuit

The series voltage regulator circuit is shown in the figure. The transistor VT is an automatic adjustment element. Since the adjustment element is connected in series in the load loop, it is called a series voltage regulator circuit. VD is a Zener diode, which provides a stable base voltage for the adjustment tube VT. R1 is the current limiting resistor of the Zener diode, and RL is the load resistor. Ui is the input voltage, U0 is the output voltage, and IC is the output current.
The selection principle of the voltage regulator tube:

1. The maximum current Izmax that the Zener tube can stabilize should be greater than 1.5 to 3 times the maximum load current ILmax.

2. The input voltage of the voltage regulator circuit is Ui > Uo, generally 2 to 3 times of Uo. The input voltage should not be too large, otherwise the current limiting resistor and Zener tube will be easily burned.