Design and implementation of digital controlled DC regulated power supply based on 51 single chip microcomputer

1 Introduction

DC regulated power supply is one of the commonly used equipment in electronic technology, and is widely used in teaching, scientific research and other fields. The traditional multifunctional DC regulated power supply has simple functions, is difficult to control, has low reliability, large interference, low precision, large size and high complexity. There are many types of ordinary DC regulated power supplies. However, they all have the following problems: the output voltage is adjusted by coarse adjustment (band switch) and fine adjustment (potentiometer). In this way, when the output voltage needs to be accurately output or needs to be changed within a small range (such as 1.02~1.03V), the difficulty is greater. In addition, with the increase of usage time, the band switch and potentiometer will inevitably have poor contact, which will affect the output. Overload is often protected by hardware with current limiting or current cutoff type, the circuit structure is complex, and the voltage stabilization accuracy is not high. This paper designs an intelligent high-precision simple DC power supply with a single-chip microcomputer as the core, which overcomes the shortcomings of traditional DC voltage sources and has high application value.

2 System Hardware Design

2.1 Overall system structure

This system is based on the AT89S51 single-chip microcomputer as the core controller. It has a digitally controlled DC power supply with preset voltage, step-by-step adjustment, and the output voltage signal and the preset voltage signal can be displayed simultaneously. Its hardware principle block diagram is shown in Figure 1. The system consists of eight parts: AT889S51 control circuit, keyboard circuit, power supply circuit, D/A circuit, power amplifier circuit, short-circuit protection and alarm circuit, voltage-stabilizing output circuit, and LED display circuit. The system controls the rise and fall of the preset voltage through the three buttons of "switch", "+", and "-", and displays it through the digital tube. The AT89S51 single-chip microcomputer sends out the corresponding digital signal, outputs the current after D/A conversion, and finally stabilizes after conversion by the integrated operational amplifier LM358, transistor amplification, and RC network filtering. At the same time, the output voltage is displayed by the LED digital tube; the measured value is measured by the digital voltmeter.

2.2 CNC part

It is mainly controlled by the AT89S51 minimum system, which has to complete the functions of keyboard control, preset voltage display control, short circuit protection control and alarm control, etc. The AT89S51 minimum system is shown in Figure 2.

2.2.1 Keyboard interface circuit

The keyboard interface circuit is shown in Figure 3. The keyboard design is controlled by three buttons: the "switch" key, the "+" key, and the "-" key, and three external pull-up resistors are connected to control the keyboard debounce. These three buttons are respectively connected to the P1.0, P1.1, and P1.2 interfaces of the microcontroller for control.

2.2.2 Preset voltage display circuit

The preset voltage display circuit is shown in Figure 4. This design uses the decoder driver 74F244 to drive the LED digital tube to display the preset voltage, which is controlled by the microcontroller P2.0~P2.7 interface. The LED common cathode control end is controlled by the P1.4~P1.6 interface, and the triode 8050 is used to control the LED display.

2.3 Power supply

2.3.1 Main power circuit

The power supply part inputs 220V, 50Hz AC power and outputs three voltages required by the whole machine: +5V, +15V, -5V, which are mainly used for the numerical control part and D/A conversion chip; +15V is used as the positive power supply of the op amp and also the main power supply of the voltage-stabilized output circuit. The power module part expands the -5V negative voltage and also serves as the negative power supply of the op amp, as shown in Figure 5.

2.3.2 Regulated output section

The voltage stabilization output part converts the voltage control word data sent by the control part into a stable voltage output. It consists of a converter (DAC0808), an integrated operational amplifier LM358, a transistor, a reference voltage source (+15V), and an overcurrent detection circuit. The voltage stabilization output module includes an overcurrent detection circuit. When the power supply is overcurrent, the overcurrent detection circuit outputs a low level and sends it to the INT0 of the CPU to request an interrupt. After the CPU receives it, it delays 5ms.

3 System Software Design

The software control program consists of two parts: the main program and the overcurrent protection program, which mainly realizes functions such as step addition and subtraction, D/A conversion, keyboard scanning, LED display, and current alarm.

3.1 Main Program

First, initialize the system, that is, initialize the AT89S51 single-chip microcomputer system, then set the system time, call the key processing subroutine to determine whether a key is pressed, if so, call the display processing program, the display processing program displays the preset voltage on the digital tube, the signal controlled by the single-chip microcomputer is converted by D/A, and then judged by the detection circuit whether it is short-circuited, if short-circuited, the interrupt protection is started. Otherwise, the voltage stabilization output is achieved. The main flow chart is shown in Figure 6.

Figure 6 Main program flow chart

3.2 Overcurrent protection procedure

The signal converted from the digital-to-analog conversion circuit passes through the current detection circuit and sends the detected signal to the single-chip microcomputer minimum system for processing. If there is overcurrent, the buzzer will sound. The overcurrent protection program flow chart is shown in Figure 7.

Figure 7 Overcurrent protection program flow chart

4 Conclusion

This design uses a single-chip microcomputer as the core to design an intelligent voltage-stabilized power supply, which is not only simple in circuit, compact in structure, low in price, but also excellent in performance. The developed intelligent voltage-stabilized power supply can use the single-chip microcomputer to set up a thorough protection monitoring system to ensure reliable operation of the power supply. The output voltage is displayed digitally, and the input is input by keyboard. The power supply has a beautiful appearance, is easy to operate, and has a high use value.