Working principle and design method of adjustable voltage-stabilized power supply

Working principle of adjustable voltage regulated power supply

When the input voltage is 150V-260V, the output voltage regulator is less than or higher than 220V, and its efficiency is reduced. The first step of control is carried out by using a single chip microcomputer to adjust and control the input voltage below 310V and above 90V within the range of 190V-250V, and a voltage stabilizer is used to stabilize the voltage.

The AC voltage of municipal power input fluctuates greatly. After the overvoltage absorption filter circuit filters out interference voltages such as high-frequency pulses, it is sent to the DC switching voltage regulator, AC sampling circuit and control execution circuit.

The power of the DC switching power supply is relatively small, but the 60-320V AC voltage can be replaced by +5V, +12V, -12V DC voltage. The +5V voltage is provided to the microcontroller, and the ±12V voltage is provided to the high-power switch module of the control circuit.

The single chip microcomputer obtains the input voltage data collected by the sampling circuit, analyzes and judges it, and sends a control signal to the trigger circuit to control and adjust the output voltage. The control execution circuit consists of an SSR zero-crossing switch high-power module and a tapped autotransformer. The SSR uses an RC buffer circuit to absorb overvoltage and overcurrent so that the SSR will not be damaged during the switching process. The control execution circuit controls the input voltage of 90-310V to the range of 190V-240V, and then sends it to the parameter regulator for precise adjustment.

The parametric voltage regulator consists of an LC oscillator, which consists of an inductor and a capacitor with an oscillation frequency of 50 Hz. No matter how the municipal electricity changes, its oscillation frequency will not change, so the output voltage remains unchanged and the voltage regulation accuracy is high. Even if the input voltage waveform is very distorted, it is a standard sine wave after oscillation by the parametric voltage regulator, so the regulated power supply has strong anti-interference and purification capabilities.

Protection alarm circuit: When the safety of the equipment is endangered, only sound and light alarms are issued to prompt the operator to take measures to avoid cutting off the output voltage. When the temperature of the control box is too high, the municipal power input is higher than 300V, and the municipal power input is lower than 130V without output voltage, there will be sound and light alarms. When the input current is too large, the input (output) air automatic switch will automatically trip.

Circuit Diagram

Circuit Schematic

Adjustable voltage regulated power supply circuit design (I)

The simple adjustable voltage-stabilized power supply uses a three-terminal adjustable voltage-stabilized integrated circuit LM317, which makes the voltage range from 1.5 to 25V and the maximum load current reach 1.5A. The circuit is shown in Figure 1.

working principle

After transformer T reduces 220V AC, 24V AC is obtained, and then 4V DC voltage is obtained through the full-bridge rectifier composed of VD33~VD1 and C1 filter. The voltage is stabilized by the integrated circuit LM317. The output voltage can be continuously adjusted by adjusting the potentiometer RP. In Figure 1, C2 is used to eliminate parasitic oscillation, C3 is used to suppress ripple, and C4 is used to improve the transient response of the stable power supply. VD5 and VD6 play a protective role when the output capacitor leaks or the adjustment end is short-circuited. LED is the working indicator of the stable power supply, and resistor R1 is a current limiting resistor. By installing a micro voltmeter PV on the output terminal, the output voltage value can be intuitively indicated.

Component selection and production

There is no special requirement for components. All you need to do is select the components according to the diagram.

Production Point

C2 should be placed as close as possible to the output of the LM317 to avoid self-excitation, which can cause unstable output voltage.

R2 should be close to the output and adjustment terminals of LM317 to avoid reference voltage changes caused by lead voltage drop between the output terminal and R2 under high current output conditions

The adjustment terminal of the voltage regulator LM317 should not be suspended, especially when connected to the potentiometer RP, to avoid the LM317 adjustment terminal from suspending due to poor contact of the sliding arm.

The capacity of C4 should not be increased arbitrarily

A heat sink should be added to the integrated block LM317 to ensure its long-term stable operation

Adjustable voltage regulated power supply circuit design (II)

The voltage of the high-current adjustable voltage-stabilized power supply can be adjusted arbitrarily between 3.5V and 25V. The output current is large and an adjustable voltage-stabilized tube circuit is used to obtain a satisfactory and stable output voltage.

• working principle

After rectification and filtering, the DC voltage is supplied to the base of the regulator tube by R1 to turn on the regulator tube. When V1 is turned on, the voltage turns on V2 through RP and R2, and then V3 is also turned on. At this time, the emitter and collector voltages of V1, V2 and V3 no longer change, and their functions are exactly the same as those of the voltage regulator. A stable output voltage can be obtained by adjusting RP, and the ratio of R1, RP, R2 and R3 determines the output voltage of the circuit.

• Component selection

Transformer T: 80W to 100W, input AC220V, output double winding AC28V.

FU1: 1A

FU2: 3A~5A

VD1 and VD2: 6A02

RP: 1W common potentiometer, resistance value range is 250K to 330K

C1: 3300 μF / 35V electrolytic capacitor

C2 and C3: 0.1 μF monolithic capacitors

C4: 470μF/35V electrolytic capacitor

R1: 180 ~ 220 Ω / 0.1W < 1W

R2, R4, R5: 10KΩ, 1/8W

V1: 2N3055

V2: 3DG180 or 2SC3953

V3: 3CG12 or 3CG80

Adjustable voltage regulated power supply circuit design (Part 3)

The power supply circuit is a 0~±15V linear adjustable voltage regulated power supply, which can be adjusted from 0V to a maximum output of ±15V. The positive power supply part uses the LM317 three-terminal adjustable integrated voltage regulator, and the negative power supply part uses the LM337 three-terminal adjustable integrated voltage regulator. The circuit has perfect current limiting, short circuit protection and thermal protection functions. Its uniqueness lies in that only one potentiometer is needed to achieve "synchronous" adjustment of positive and negative voltages. It has the characteristics of simple circuit, convenient adjustment, excellent performance and low cost. Therefore, it is very suitable for electronic enthusiasts to DIY.

• working principle

The whole circuit is shown in the figure. The input part of the power supply is a common transformer step-down and bridge rectifier, which add capacitor filters and obtain ±22V DC voltage that is symmetrical up and down. Another two sets of ±6.8V auxiliary voltages are also derived and connected to the V+ and V- terminals of operational amplifier IC4 and operational amplifier IC3 respectively to ensure that the operating voltage of IC3 and IC4 does not exceed the limit range. The following is a specific description of the voltage stabilization part:

— The positive output circuit consists of the regulator IC1 and related components, which are usually connected to the adjustment terminal of the regulator IC1, and the other terminals of the potentiometer are grounded. If the value of the RP1 resistor is adjusted to 0, the output voltage Vout is 1.2V, and a 3mA constant current is generated on the resistor R10. As long as the resistance value of RP1 is changed, the output voltage can be changed.

Here, the ground terminal of RP1 is changed to the output terminal of the operational amplifier IC3. The output voltage of IC3 is -1.2V, which is used to offset the reference voltage of IC1 by +1.2V, thereby realizing modulation starting from 0. It is also very simple to achieve the above purpose. We only need to connect the operational amplifier IC3 to the differential amplifier and complete the subtraction operation. As can be seen from the figure, the in-phase input voltage is V1, and the reverse input voltage is V2. Since R4=R5=R6=R7, the output voltage of IC3 is VO=R5/R4×(V1-V2)=-1.2V, and the output voltage of the regulator IC1+Vout=5mA×R3+10mA×PR1-1.2V.

— The negative output circuit consists of the voltage regulator IC2 and related components, omitting the potentiometer RP3, which was originally set on the adjustment terminal of IC4 and is now connected to the output of the operational amplifier IC4 to control the output voltage of the adjustment terminal. The purpose of adjusting the output voltage of the voltage regulator can also be achieved. Since the operational amplifier IC1 is connected as an inverting amplifier with a gain of 10 and its inverting input is connected to the output of the positive output circuit voltage regulator, the negative output voltage stabilizer produces a stable voltage with opposite polarity and equal amplitude. That is, -Vout=-R9/R9 × (+Vout),). Because R10=R《, -Vout=+Vout. Therefore, the negative output voltage tracks the positive output voltage.

— The diodes D7 and D8 in the circuit are used to prevent the increase of the capacitance discharge of the external load, which will cause damage to the output of IC1 and IC3; in addition, the diodes D9 and D10 are used to prevent the adjustment terminals of IC1 and IC2 from breaking down due to the positive saturation of the output of IC3 and the negative saturation of the output of IC4. This is because the adjustment terminals of IC1 and IC2 do not allow reverse current to flow into them.

• Component selection

This machine is all common parts, no special specifications. IC1 and IC2 are three-terminal adjustable integrated voltage regulators, the positive output model is LM317, and the negative output model is LM337. Their packaging is TO-220, both of which are available on the market. The heat sink should be installed when it is put into use. IC3 and IC4 are general-purpose operational amplifiers, and can also be replaced by OP-07. The resistors are all 1/4W metal film resistors, among which R4, R5, R6, R7, R9, and R10 have an accuracy of 1%. RP1 should use a winding potentiometer, and a multi-turn potentiometer will be better. The power transformer T can choose a 14-inch black and white TV power transformer. If you want to wind it yourself, you should choose an EI type Gaoxi steel plate, and the power range can be 35W-45W.

Adjustable voltage regulated power supply circuit design (IV)

In this power supply, LM317 is used as a voltage regulator, and an adaptive switching circuit is used to automatically switch the input voltage according to the output voltage, thereby reducing the voltage difference between the input voltage and the output voltage and reducing the power consumption of the power supply itself. Among them, VT2, VD5, Volkswagen, R5, R6, C10 and relay K form an adaptive switching action circuit. When the output voltage Vo is lower than 14V, VW is cut off due to insufficient breakdown voltage and no current passing.

VT2 is cut off and K does not work. Its contact K-1 is normally closed, and the secondary 14VAC of the transformer is connected to the voltage stabilizing circuit. On the contrary, when the output voltage is greater than 14V, VW breaks down and VT2 is turned on. K obtains power, K-1 acts, and 28V AC voltage is connected to the voltage stabilizing circuit. Therefore, the input and output voltage difference does not exceed 15V. The output voltage of the circuit is 1.25V~30V, which is continuously adjustable, and the maximum output current is 3A. As shown in Figure 7, it is an adaptive adjustable voltage stabilizing power supply circuit based on LM317:

Adjustable voltage regulated power supply circuit design (V)

The main device of the DC adjustable voltage-stabilized power supply with overcurrent protection is the universal voltage-stabilized integrated block LM723, which includes a startup circuit, a constant current source, a reference voltage-stabilized source, overcurrent protection, etc. With a high-power regulating tube, it can output a continuously adjustable stable voltage in the range of 0 to 20. The maximum output current can reach 2A, and it has an overcurrent protection function. It can be used as a maintenance power supply for mobile phones and BP machines, and can also be used for battery charging. The circuit is shown in Figure 9.

In normal use, the red and green LEDs light up at the same time. The output voltage can be adjusted within the range of 0~20 by adjusting the potentiometer W. When there is an overcurrent or short circuit at the output end, the voltage drop across R1 is greater than 0.6V, Q3 and Q4 are turned on, the green light goes out, the LM723 voltage drops to nearly 0V, the internal detection circuit works, and the output 23V high voltage and Q1, Q2 are cut off.

Therefore, there is no voltage output, which plays a protective role. The output is available only when the computer is shut down and restarted. In order to ensure that the regulating tube Q1 will not burn out when outputting the rated current, a heat sink of sufficient size should be installed. The entire power supply can use a plastic box as the shell, and its front plate can be equipped with an ammeter, a voltmeter, a switch and a potentiometer, output terminals and red and green light-emitting diodes. As long as the components are good, the circuit can work normally without debugging. Among them, it is best to use imported C2819, 2N3395 and other high-power tubes as Q1, and LM723, MC1723, etc. can be used as ICs.