DC voltage regulator as a provider of DC energy, has an extremely important role in a variety of electronic equipment, whether its performance is good or not directly affects the accuracy, stability and reliability of electronic products. 

This paper analyzes the principle of regulated power supply, selects the design scheme of regulated power supply, constructs the circuit diagram of DC power supply and selects suitable components, and finally designs a DC voltage regulator with adjustable output voltage.

Definition of DC Voltage Regulator

The electronic device that can provide stable DC power to the load is called DC voltage regulator. Due to the characteristics of electronic technology, the power supply circuit is required to provide continuous and stable power to the electronic equipment to meet the requirements of the load, and it is usually required to provide stable DC power, and the power supply that provides such stable DC power is DC voltage regulator.

Technical Indexes of DC Voltage Regulator

The main technical indexes of DC voltage regulator are: output rated voltage, output rated current, output voltage range, voltage adjustment rate, voltage regulation coefficient Sr, output resistance Ro and ripple coefficient.

Output Rated Voltage and Range

220V AC input voltage changes in the range of 198V ~ 240V or so, the output voltage of the regulated power supply will not be affected by the input voltage is too large, in the input voltage in the range of changes in the output voltage change is only a few millivolts.

Output Rated Current

Output rated current is an important indicator to reflect the voltage stabilized source, the voltage stabilized source, variable resistor, digital multimeter in series, with a variable resistor to simulate the load, adjust the resistor value so that the current for the design of the rated value, and then reduce the resistance value, the current will be greater, and the output voltage change is very small, but when you continue to reduce the resistance to a certain value, the output voltage began to drop sharply, then the current value is the maximum output current. The current value is the maximum output current.

Voltage Regulation Coefficient Sr

Voltage regulator voltage coefficient Sr definition: when the load is unchanged, the relative change in the output DC voltage Uo and the relative change in the input DC voltage UI ratio, the smaller the Sr, the better the voltage regulator performance.

Voltage Regulation Rate

Generally, the fluctuation limit of the grid voltage is ±10%, under this condition (ΔUI/UI=±10%), the relative change of output voltage ΔUO/UO is measured, which is called the voltage regulation rate.

Ripple Coefficient

Ripple coefficient is the peak-to-peak value of the AC component in the DC voltage, as the DC stabilized power supply is generally formed by the AC power supply through the rectifier regulator and other links, it is inevitable that the DC stabilized amount of more or less with some AC components, this superimposed on the DC stabilized amount of the AC component is called ripple.

Output Resistance Ro

Reflects the ability of the regulated power supply with load, defined as: when the input voltage is unchanged, due to load changes caused by the output DC voltage changes and the output DC current changes than the ratio, the smaller the Ro, indicating that the regulated power supply with load the stronger the ability.

Response Speed

DC voltage regulator in the rated operating conditions, when the input voltage or load changes dramatically, the voltage back to the normal value of the time required, the response speed is also an important quality indicator of DC voltage regulator.

Classification of Voltage Regulator

DC voltage regulator can be divided into chemical power supply, linear regulated power supply and switching regulated power supply.

Chemical Power Supply

Dry batteries, lead-acid batteries, nickel-cadmium, nickel-metal hydride, lithium-ion batteries are chemical power.

Linear DC Voltage Regulator

Linear DC voltage regulator refers to the DC voltage regulator where the regulator works in a linear state. Linear DC voltage regulator mainly includes industrial frequency transformer, output rectifier filter, control circuit, protection circuit and so on.

Switching DC Voltage Regulator

Switching DC voltage regulator is the use of control switching transistor turn on and off time ratio, to maintain a stable output voltage of a power supply. Its circuit form mainly includes single-ended flyback, single-ended forward, half-bridge, push-pull and full-bridge. Its advantages are small size, light weight, stability and reliability; disadvantages relative to linear DC voltage regulator, its ripple is larger.

DC Voltage Regulator Design

Principle

Linear DC voltage regulator is the first AC power through the transformer voltage, and then rectified by the rectifier circuit rectifier filter to get the unstabilized DC voltage, in order to achieve high precision DC voltage, must then adjust the output voltage after the voltage feedback, you can achieve a very high degree of stability, the ripple is also very small, and there is no switching regulated power supply has the interference and noise.

Component

Resistance

Resistance is the most common component used in all electronic circuits, and represents the amount of resistance a conductor has to a current. Resistive elements are energy-consuming components that present a barrier to current flow. The resistance value of a resistive element is generally related to temperature, material, length, and cross-sectional area, and the temperature coefficient is a physical measure of how much the resistance is affected by temperature, which is defined as the percentage change in resistance value for every 1°C rise in temperature.

Capacitance

Capacitor is a static charge storage medium, is an indispensable electronic component in the field of electronics and electric power. It is mainly used in power supply filtering, signal filtering, signal coupling, resonance, filtering, compensation, charging and discharging, energy storage, DC isolation and other circuits.

Voltage Regulator Diode

Voltage regulator diode is a kind of semiconductor device with high resistance until the critical reverse breakdown voltage, in this critical breakdown point, the reverse resistance is reduced to a very small value, in this low resistance area the current increases while the voltage is kept constant, the voltage regulator diode is graded according to the breakdown voltage, because of this characteristic, the voltage regulator tube is mainly used as a voltage regulator or voltage reference element.

Transformer

Transformer is the use of the principle of electromagnetic induction to change the AC voltage device, the main components are the primary coil, secondary coil and core (core). The main functions are: voltage conversion, current conversion, impedance conversion, isolation, voltage stabilization (magnetic saturation transformer) and so on.

Design Analysis

According to the principle of DC voltage regulator, we design an adjustable DC voltage regulator, the output DC voltage range is: +4V~+9V, the maximum output current I=0.9A, the output voltage variation: <0.005V, the regulator coefficient S<0.003. The design power supply consists of four parts: the power transformer, the rectifier circuit, the filtering circuit, and the regulator circuit, and the functions of its components are described below. The role of the components is described as follows.

Rectifier Filter Circuit

The filter circuit is used to filter out the ripple in the output voltage and is generally composed of reactance elements. As the reactance element in the circuit has the role of energy storage, parallel capacitance power supply voltage increases, can be part of the energy stored, and when the voltage decreases, the energy can be released, so that the load voltage is relatively smooth.

Voltage Regulator Circuit

The function of the voltage regulator circuit is to maintain the output DC voltage stable when the grid voltage fluctuates and the load temperature changes.

Design Program

Rectifier Circuit Selection

1. Single-phase full-wave rectifier circuit

The rectification period used is twice as much as that of half-wave rectification, and the rectification voltage pulsation is smaller than that of half-wave rectification. The output voltage Vo=0.9Vi without filter circuit, the utilization rate of transformer is higher than that of half-wave rectifier, and the reversed voltage during rectification is higher.

2. Single-phase bridge rectifier circuit

Use of the rectification period than the full-wave rectifier more than double the rectifier voltage pulsation and full-wave rectifier is the same, each period of the reverse voltage borne by the power supply voltage peak, the transformer utilization is higher than the full-wave rectifier circuit.

Voltage Regulator Circuit Selection

1. Simple parallel type voltage stabilized power supply

Shunt type voltage regulator regulator is connected in parallel with the load, thus it has very low output resistance, good dynamic characteristics, simple circuit, and automatic protection function, load short circuit regulator cut-off, high reliability, single efficiency bottom, especially in small current regulator needs to withstand a large amount of current, loss is too large.

2. Fixed three-terminal regulator

By the fixed three-terminal regulator output pin, input pin and ground pin, LM317 is an adjustable voltage regulator chip, the input side of the capacitor can be further filtered, the output side of the capacitor can be improved to improve the instantaneous impact of the load, this circuit is more stable.

Conclusion

After the principle of DC voltage regulator and analysis and design, we conclude that when the AC power supply voltage or load resistance changes, the DC output voltage regulator will remain stable; but the constant voltage source does not exist, it is only an ideal state, although the output voltage can be basically stable, but it is not a little bit unchanged, and aging or environmental changes in the components will lead to load impedance has a certain change. It is only an ideal state, although the output voltage can be basically stabilized, it is not constant. DC voltage regulator in the power supply technology occupies a very important position, with the development of electronic equipment to the direction of high precision, high stability and high reliability, the power supply requirements of electronic equipment will be increasingly high.