Design of short distance wireless power supply device based on C51

Abstract: This paper is based on wireless power supply module, which consists of power transmitting circuit, receiving circuit, detection circuit. And this paper mainly introduces the wireless transmission system based on C51 MCU application efficiency of detection, and realize the wireless transmission function. Meanwhile, it has high transmission efficiency and reach the expected goal.

Keyword：Wireless power supply, C51, Transmission efficiency

1 Introduction

Wireless power supply is a convenient and safe power supply device that does not require any physical connection. When the frequency of the oscillating magnetic field generated by the transmitter is the same as the natural frequency of the receiver, the receiver will resonate, thereby achieving energy transmission. It has now been used in some small household appliances and may be used for indoor power supply and urban power supply in the near future, completely replacing wires and having broad application prospects. This article mainly describes short-range wireless power supply, which has the characteristics of low power consumption and safety, and its reliability is better increased through single-chip microcomputer detection [1].

2 System Design

Design and production of wireless power supply demonstration device. The circuit consists of three parts: power transmission circuit, receiving circuit, and detection and display circuit [2].

2.1 Scheme demonstration and selection

Solution 1: Oscillator circuit

The transmitting circuit uses NE555 to generate a symmetrical square wave with adjustable frequency, and then connects to L298 amplification and constant current source module to generate a square wave signal with voltage of 12V and frequency of 20MHZ as the transmitting part. The receiving part is composed of a large inductor coil and a rectifier Schottky diode. The detection part is controlled by STC89c51 to collect voltage and current signals through AD tcl2543 [3].

This solution has a simple circuit structure, fewer components, is easy to control and has low cost.

Solution 2: Chopper Circuit

The transmitting circuit uses IGBT to invert the DC power supply, perform chopping control, and generate an AC signal as the transmitting signal. The receiving part is the same as scheme 1, and the detection part mainly uses MAX197 as the AD chip.

This solution has a simple structure, but the switching frequency of the IGBT is difficult to control and the price of the IGBT is not suitable.

Compared with the above schemes, the oscillation circuit structure is simple and easy to implement, the price of the AD chip of the detection part is reasonable, and the whole circuit is easy to implement, so we choose scheme 1. The overall block diagram of the system is shown in Figure 1.

Figure 1 System overall block diagram

2.2 Overall circuit design

(1) Transmitter circuit

Use NE555 to generate a symmetrical square wave with adjustable frequency, connect L298 amplification and constant current source module to generate a square wave signal with a voltage of 12v and a frequency of 20MHZ as the oscillation part, mainly to generate high frequency.

(2) Power output circuit

Since the output drive signal voltage, current, and frequency are large, a certain output power is required to drive the coil, so a power output circuit is needed in the end. You can use discrete high-power transistors to build the output circuit, or you can use a motor drive bridge circuit integrated module. When choosing, you need to pay attention to the frequency response of the circuit should be greater than 20kHz, and the output power should be greater than 2W.

(3) Current control

The current control circuit controls the output current to be stable at around 100mA and does not fluctuate with changes in the power supply. Constant current output control does not require special precision. In general, when the requirements are not high, a current limiting resistor can be used to control the stability of the current.

Figure 2 Oscillator circuit and transmitter circuit

(4) Power supply

The power supply circuit is shown in Figure 3.

Figure 3 Partial circuit of power supply circuit

(5) Receiving circuit

The receiving part is composed of a large inductor coil and a rectifier Schottky diode.

Figure 4 Receiving circuit

(6) Detection circuit and microcontroller selection

The AD chip TCL2543 of STC89C51 and 12 meets the requirements and is cheap. The display part uses 1602 to display the detected voltage and current.

Figure 5 Control detection and display circuit

3. Hardware circuit production and component selection

3.1 Selection of power supply

The input DC voltage is 8 volts higher than the voltage of the battery being charged. As shown in Figure 3, R1, Q1, W1, and TL431 form a precision adjustable voltage regulator circuit, Q2, W2, and R2 form an adjustable constant current circuit, and Q3, R3, R4, R5, and LED are charging indication circuits. As the voltage of the battery being charged rises, the charging current will gradually decrease. When the battery is fully charged, the voltage drop on R4 will decrease, causing Q3 to be cut off and the LED to go out. To ensure that the battery is fully charged, continue to charge for (1-2) hours after the indicator light goes out. When using, install a suitable heat sink on Q2 and Q3. The advantages of this circuit: simple to make, easy to purchase components, safe charging, intuitive display, and will not damage the battery. By changing W1, multiple lithium batteries in series can be charged, and by changing W2, the charging current can be adjusted over a wide range. The disadvantage is that there is no overcurrent discharge control circuit.

3.2 Selection of Transmitter Circuit Components

(1) The oscillation circuit is composed of NE555 and L298, because NE555 can generate a maximum of 500MHE, which is enough to generate the power we need after being amplified by L298.

F =1.44/(R1+RP1)C2 (1)

The frequency of the 555 chip can be controlled according to the above formula.

(2) Coupling coil in the transmitting circuit

Production of the transmitting coil: Wrap 20 turns on a 40mm diameter ring, (25~30)μH (the receiving output current is large when the inductance is small, and the receiving output current is slightly smaller when the inductance is large). The operating current of the transmitting module automatically increases or decreases with the size of the receiving load current.

3.3 Selection of receiving circuit components

(1) Fabrication of the receiving coil

The receiving coil is wound with the same number of turns as the transmitting coil. After determining the distance, adjust the number of turns of the coil until the receiving voltage is slightly higher than the load. The receiving coil outputs a high-frequency AC voltage, which can directly power a small light bulb. To power other electrical appliances, it must pass through a switching voltage regulator module to output a DC 5V working voltage. If working with a small current, the number of turns of the receiving coil can be appropriately increased to increase the transmission distance.

(2) The rectifying Schottky diode constitutes the rectifying circuit of the receiving circuit, and a light-emitting diode is connected to serve as the indicator light of the receiving circuit.

4 System software design process

The system program flow is shown in Figure 6.

Figure 6 System flow chart

Programming in C language is convenient, concise, easy to modify and simple to control[4].

5 Conclusion

This paper designs a wireless power supply module based on 51 single-chip microcomputer. This module has the characteristics of high transmission efficiency and can be used as a power supply system for small short-distance controllers. It is simple to make and has strong practicality. It has broad application prospects in the electronics industry.

References

[1] Chen Zhiwang and Chen Zhiru. 51 Series Single Chip Microcomputer System Design and Practice[M]. Publishing House of Electronics Industry, 2009.2.

[2] Wang Hongjun. Principles and Applications of Single Chip Microcomputers[M]. Shandong University Press, 2009.2.

[3] He Limin. MCS-51 Series Single Chip Microcomputer Application System Design System Configuration and Interface Technology [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 1990.

[4] Zhang Junmo. Intermediate Tutorial of Single-Chip Microcomputers[M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2002.

About the Author

Hao Tao, born in August 1985, male, Han nationality, from Weifang City, Shandong Province,

A master's student at Shandong University of Light Industry, engaged in research on detection devices and automation technology. ■