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　　What is a circuit regulator? Analysis of the working principle of the circuit voltage regulator, and analysis of the circuit principle of the switching circuit voltage regulator

　　How circuit regulators work

　　Voltage stabilization The process of stabilizing the output voltage by using the adjustment function of the circuit is called voltage stabilization.

　　A voltage stabilizing circuit is a circuit that can maintain a constant output voltage when the input voltage, load, ambient temperature, circuit parameters, etc. change. This circuit can provide stable DC power and is widely used in various electronic equipment.

　　Basic components of a circuit regulator

　　Adjustment components, reference voltage circuit, sampling circuit, comparison amplifier circuit

　　Classification of regulated power supplies There are many classification methods for regulated power supplies. According to the type of output power supply, they are divided into DC regulated power supplies and AC regulated power supplies;

　　Switching circuit regulator circuit analysis

　　The connection methods between the voltage stabilizing circuit and the load are divided into series regulated power supplies and parallel regulated power supplies; according to the working state of the regulating tube, they are divided into linear regulated power supplies and switching regulated power supplies; according to the circuit type, they are divided into simple regulated power supplies and feedback type Stabilized power supply, etc. Such a large number of classification methods often make beginners confused and don't know where to start. In fact, it should be said that there is a certain hierarchical relationship between these seemingly numerous classification methods. As long as this level is clarified, the types of power supplies can naturally be distinguished.

　　The principle of switching-type regulated power supply can be illustrated by the circuit in Figure 1. It consists of adjustment tube, filter circuit, comparator, triangle wave generator, comparison amplifier and reference source.

　　The triangle wave generator generates a square wave vB through the comparator to control the on and off of the adjustment tube. When the regulating tube is turned on, it charges the inductor. When the regulating tube is turned off, a discharge path must be provided for the current in the inductor. The freewheeling diode D can play this role and is helpful to protect the adjustment tube. According to the wiring of the circuit diagram, when the amplitude of the triangular wave is smaller than the output of the comparison amplifier, the comparator outputs a high level (the part of the output waveform whose potential level is higher than the minimum value of the high level, for a square wave, is equivalent to the part where the square wave exists ). The conduction time of the corresponding adjustment tube is, on the contrary, it is low level (the part of the output waveform whose potential level is lower than the maximum value of the low level, for a square wave, is equivalent to the part where the square wave does not exist). The cut-off time of the corresponding adjustment tube is toff.

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　　In order to stabilize the output voltage, feedback should be introduced in the form of voltage negative feedback to determine the connection between the reference source and the comparison amplifier. Assume that the output voltage increases, FVO increases, the output VF of the comparison amplifier decreases, the square wave output toff of the comparator increases, the conduction time of the adjustment tube decreases, and the output voltage decreases. Plays a voltage stabilizing role.

　　The waveforms of each point are shown in Figure 2. Since the output of the emitter of the adjustment tube is a square wave, the presence of the filter inductor makes the output current iL a sawtooth wave, which tends to be smooth. The output is a rippled DC voltage.

　　Neglecting the DC resistance of the inductor, the output voltage VO is the average component of vE. So there is q called the duty cycle, which is the percentage of the high level time of the square wave in the entire cycle. When the input voltage is constant, the output voltage is proportional to the duty cycle, and the output voltage value can be controlled by changing the width (duty cycle) of the comparator output square wave. This control method is called pulse width modulation (pWM).

　　From the above analysis, the following conclusions can be drawn:

　　1. The adjustment tube works in the switching state, the power consumption is greatly reduced, and the power efficiency is greatly improved;

　　2. The regulating tube works in a switching state. In order to obtain DC output, a filter must be added to the output end;

　　3. The output voltage value can be easily changed by controlling the pulse width;

　　4. The power transformer can be eliminated in many situations;

　　5. Due to the high switching frequency, the size of the filter capacitor and filter inductor can be greatly reduced.

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