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Analysis of four voltage stabilizing circuits
The fluctuation of ac network voltage and the change of load current will make the output voltage and current of rectified power supply change accordingly, so the electronic circuit with higher requirements must use the stabilized power supply.

(1) Parallel voltage regulator tube voltage regulator circuit

The circuit that USES a regulator tube in parallel with the load is the simplest regulator circuit as shown in Figure 4 (a). In the figure R is the current limiting resistance. The output current of this circuit is very small, and its output voltage is equal to the stable voltage value of the regulator tube, V and Z.

(2) Series voltage regulator circuit

The series voltage regulator circuit with amplification and negative feedback is the most common regulator circuit. Its circuit and block diagram are shown in FIG. 4 (b) and (c). It detects the variation of the output voltage from the sampling circuit (R3 and R4), compares it with the reference voltage (V Z), amplifies it through the amplifier (VT2), and then adds it to the regulating tube (VT1), so that the voltage at both ends of the regulating tube changes with the change. If the output voltage is lowered, so is the voltage drop in the regulating tube, so that the output voltage is raised; If the output voltage goes up, so does the voltage drop in the regulating tube, so that the output voltage is lowered, leaving the output voltage essentially unchanged. On the basis of this circuit, it has been developed into many types of circuits or added some auxiliary circuits, such as the composite tube as the regulating tube, the circuit with adjustable output voltage, the circuit with operational amplifier as the comparison amplifier, and the auxiliary power supply and the overcurrent protection circuit.

(3) Switching voltage regulator circuit

In recent years, a new type of stabilized voltage supply is widely used as a switching stabilized voltage supply. Its adjusting tube works in the switching state, the power consumption itself is very small, so high efficiency, small size and other advantages, but the circuit is more complex.

There are many kinds of switch regulator power supply from the principle. Its basic principle block diagram is shown in FIG. 4 (d). In the figure, inductor L and capacitor C are energy storage and filter elements, while diode VD is a continuation diode that provides a current path for L and C filters when the regulating tube is turned off. The switching frequency of the switching regulator power supply is very high, generally a few ~ tens of kilohertz, so the volume of the inductor is not very large, the output voltage of the high harmonic is not much.

Its basic working principle is: the sampling voltage detected from the sampling circuit (R3, R4) is compared and amplified to control a rectangular wave generator. The output pulse of the rectangular wave generator controls the on and off time of the regulating tube (VT). If the output voltage U 0 is reduced due to changes in the grid voltage or load current, the output pulse of the rectangular wave generator will be widened. Therefore, the regulating tube conduction time will be increased, so that the L and C energy storage circuits will get more energy. As a result, the output voltage U 0 will be increased to achieve the purpose of stabilizing the output voltage.

(4) Integrated voltage regulator circuit

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

The integrated voltage regulator has only three terminals, and all parts of the regulator circuit, including the high-power regulator and protection circuit, have been integrated into the chip. When used, as long as the heat sink connected to the rectifier filter circuit behind the line. Few peripheral components, high voltage stability accuracy, reliable work, generally do not need debugging.


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



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