1. Introduction to the principle
The wireless charging system mainly utilizes the principle of electromagnetic induction. The electromagnetic induction scheme uses the transformer principle to realize the transmission of electric energy through the induction of the primary and secondary coils. The wireless energy transmission system based on this method mainly has three major components, namely, an energy transmitting end, a contactless transformer, and an energy receiving end. When an alternating current is passed through the transmitting coil, the current will form an alternating magnetic field in the surrounding medium, and the induced electromotive force generated in the receiving coil can supply power to the mobile device or charge the battery. The feature of this solution is that the energy receiving end is connected to the secondary coil, can be flexibly moved, the circuit is simple, and easy to implement, and can be used in places where the distance requirement is not high but mechanical and electrical connections are not required.
2, system design
2.1 overall design
The wireless charging system consists of a power supply circuit, a high-frequency oscillating circuit, a high-frequency power amplifying circuit, a transmitting and receiving coil, and a high-frequency rectifying and filtering circuit. The system frame is as shown in the following figure (1), and finally the rechargeable battery is charged. From the principle of wireless circuit transmission, electric energy and magnetic energy propagate in space with electromagnetic waves in the form of electromagnetic waves. In order to generate electromagnetic waves, electromagnetic oscillations must first be generated. The higher the frequency of electromagnetic waves, the higher the intensity of radiation to space. The larger the electromagnetic oscillation is at least higher than 100KHZ, there is enough electromagnetic radiation.
2.2 High frequency oscillation circuit design
Two crystal oscillation circuits composed of a crystal oscillator circuit CD4069 of a CMOS circuit six-inverter CD4069 are shown in Fig. (2).
Producing high frequency oscillation with CD4069 is better than LC oscillator circuit
2.3 Power amplifier design
The circuit is shown in Figure (3)
The FET is a voltage control component and is a triode similar to a tube. Compared with a bipolar transistor, a field effect transistor has high input impedance, low input power consumption, good temperature stability, good signal amplification stability, and signal. The distortion is small, the noise is low, and the amplification characteristics are better than the electronic triode. In the figure (3), the three resistors R1, R2 and R3 in the power FET circuit are connected in parallel to the gate G of the FET, and the front stage is high. The frequency oscillating circuit is also connected to G; the original stage S is directly grounded; the drain D is connected to the LC oscillating circuit, and its resonant frequency is the same as the high frequency oscillating frequency of the previous stage.
2.4 Transmit and Receive Coil Circuit Flowchart 4 as shown below
Both the transmitting and receiving coils are wound around 12 turns with an enameled wire of about 0.5 ram in diameter, and the coil has a diameter of about 80 rpm. The function of the transmitting module is to efficiently convert the DC energy into a radio frequency power signal, so that the receiving circuit can fully utilize the module that the energy receiving module processes after receiving the energy of the previous stage. In order to meet the needs of practical applications, the received RF signal needs to be rectified, filtered, stepped down, and stabilized. The DC voltage after processing can be used by other loads. The module mainly includes a rectifier circuit and a step-down circuit.
2.5 wireless power supply circuit selection program
A wireless charging circuit consisting of a crystal oscillator circuit and a power FET of the CD4069.
The circuit is shown in Figure (6)
The charging circuit's CD400 series CMOS circuit has a limit voltage of 18v, and the unstable AC 12V voltage rectified and filtered no-load voltage may exceed 18v, so the CD4069's power supply voltage is provided by a three-terminal regulator IC 7805. All unused input terminals of the CMOS circuit are connected to appropriate logic levels, and the crystal oscillator is connected to a single-gate oscillator. The oscillating output is buffered by the second stage and sent to the gate G of the power FET to start to protect the FET. Bias and leakage circuits are placed on the pole circuit to ensure stable operation of the circuit.
3. Experimental steps
Connect the lines as shown below and connect them for debugging.
4, design summary
This experiment can illuminate the light-emitting diode and can charge the rechargeable battery, basically meeting the experimental requirements, but the sensing distance between the transmitting coil and the receiving coil is not too long, so there is room for improvement. For example, a power amplifying circuit can be connected to the transmitting circuit to increase the power of the transmitting coil.
5, simulation diagram
Before simulation:
After the simulation:
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