How to quickly interpret the circuit's voltage regulator circuit

- Dec 30, 2019-

How to quickly interpret the circuit's voltage regulator circuit

If you want to learn the knowledge of electronic circuits, the recognition of circuit diagrams is a must. However, it is difficult for many novices to master the reading of circuit diagrams in a short time. At this point, you need to plan the circuit diagram to make it easy to understand. This article will introduce the characteristics and structure of the voltage regulator circuit in the circuit diagram.

 

  Regulator circuit

 

The fluctuation of the AC grid voltage and the change of the load current will cause the output voltage and current of the rectifier power to change accordingly. Therefore, electronic circuits with higher requirements must use a regulated power supply.

 

Voltage regulator circuit in parallel

How to quickly interpret the voltage regulator circuit of the circuit diagram

 

The circuit that uses a voltage regulator tube in parallel with the load is the simplest voltage regulator circuit, see Figure 1 (a). In the figure, R is the current limiting resistor. The output current of this circuit is very small, and its output voltage is equal to the stable voltage value VZ of the Zener.

 

Series voltage regulator circuit

 

 The series regulator circuit with amplification and negative feedback is the most commonly used regulator circuit. Its circuit and block diagram are shown in Figure 1 (b), (c). It detects the change of output voltage from the sampling circuit (R3, R4), compares it with the reference voltage (VZ) and amplifies it by the amplifier (VT2), and then adds it to the adjustment tube (VT1). Variety. If the output voltage drops, the pressure drop of the pass tube is also reduced, so the output voltage is increased; if the output voltage rises, the pressure drop of the pass tube is also increased, so the output voltage is reduced, and the output voltage is basically unchanged . Based on this circuit, many variant circuits or additional auxiliary circuits have been developed, such as the use of a composite tube as a regulating tube, a circuit with adjustable output voltage, an operational amplifier as a comparative circuit, and an auxiliary power supply and overcurrent protection circuit Wait.

 

Switching regulator circuit

 The new type of stabilized power supply widely used in recent years is a switching-type stabilized power supply. Its pass transistor works in the on-off state, and its power consumption is very small, so it has the advantages of high efficiency and small size, but the circuit is more complicated.

There are many types of switching regulated power supplies in principle. Its basic principle block diagram is shown in Figure 1 (d). In the figure, the inductor L and capacitor C are energy storage and filtering elements, and the diode VD is a freewheeling diode that provides a current path for the L and C filters when the pass transistor is in the off state. The switching frequency of the switching stabilized power supply is very high, generally several to several tens of kilohertz, so the volume of the inductor is not very large, and there are not many high-order harmonics in the output voltage.

Its basic working principle is: the sampling voltage is detected from the sampling circuit (R3, R4) and compared to amplify to control a rectangular wave generator. The output pulse of the rectangular wave generator is used to control the on-time and off-time of the pass transistor (VT). If the output voltage U0 decreases due to changes in the grid voltage or load current, the output pulse of the rectangular wave generator will be widened, so the turn-on time of the adjustment tube will increase, and the L and C energy storage circuits will get more energy. As a result, the output voltage U0 is increased, and the purpose of stabilizing the output voltage is achieved.

Integrated voltage regulator

 

In recent years, a large number of integrated voltage stabilizer products have come out, with many varieties and different structures. At present, three-terminal integrated voltage regulators are widely used, including CW7800 series outputting positive voltage and CW7900 series outputting negative voltage. The output current is from 0.1A to 3A, and the output voltage is 5V, 6V, 9V, 12V, 15V, 18V, 24V and so on.

 

This integrated voltage regulator has only three terminals, and all parts of the voltage regulator circuit, including high-power regulator tubes and protection circuits, have been integrated into the chip. When using, just add a heat sink and connect it behind the rectifier and filter circuit. Fewer peripheral components, high voltage stabilization accuracy, reliable operation, and generally do not need debugging.

Figure 1 (e) is a three-terminal regulator circuit. In the figure, C is the main filter capacitor, C1 and C2 are capacitors to eliminate parasitic oscillation, and VD is a protection diode used to prevent the input short circuit from burning out the integrated block.

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    As can be seen from the introduction above, the voltage stabilization circuits in the circuit are basically divided into 4 types. As long as you master these 4 circuit forms, you can easily identify the voltage regulator circuit in the circuit diagram. The more types of circuits that can be identified, the more accurate and fast the interpretation of the circuits will be. I hope everyone can gain something after reading this article.


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