Simple and practical wireless charger design

The basic function is to transmit electrical energy to the battery wirelessly through the coil. Simply place the battery and the receiving device on the charging platform to charge it. Experiments have shown that although the system cannot charge invisibly, it can place multiple school appliances on the same charging platform and charge them at the same time, eliminating the trouble of wiring.

1 Principle and structure of wireless charger
The wireless charging system mainly adopts the principle of electromagnetic induction, and realizes energy transfer through energy coupling through coils. As shown in Figure 1, when the system is working, the input end converts the AC mains into DC through a full-bridge rectifier circuit, or uses a 24V DC terminal to directly power the system. The DC power output after passing through the power management module is converted into high-frequency AC power by a 2M active crystal oscillator inverter to supply the primary winding. Energy is coupled through two inductor coils, and the current output by the secondary coil is converted into DC power through a receiving conversion circuit to charge the battery.

2.2 Transmitter circuit module
is shown in Figure 3. The main oscillator circuit uses a 2 MHz active crystal oscillator as the oscillator. The square wave output by the active crystal oscillator is filtered out by a second-order low-pass filter to remove high-order harmonics, and a stable sine wave output is obtained. After passing through the Class C amplifier circuit composed of the transistor 13003 and its peripheral circuit, it is output to the parallel resonant circuit composed of the coil and the capacitor to radiate out, providing energy for the receiving part.

2.2 Receiving circuit module
The wire diameter of the air-core coupling coil of the parallel resonant circuit composed of the capacitor is measured to be 0.5 mm, the diameter is 7 cm, the inductance is 47 uH, and the carrier frequency is 2 MHz. According to the parallel resonance formula, the matching capacitor C is about 140 pF. Therefore, the transmitting part uses a 2MHz active crystal oscillator to generate an energy carrier frequency close to the resonant frequency.

2.3 Charging Circuit