Wireless charger design

1 Principle and structure of wireless charger

The wireless charging system mainly uses the principle of electromagnetic induction to achieve energy transfer through energy coupling through coils. As shown in Figure 1, when the system is working, the input terminal converts the AC mains power into DC power through the full-bridge rectifier circuit, or uses the 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 and supplied to the primary winding. The energy is coupled through the two inductors, and the current output by the secondary coil is converted into direct current by the receiving conversion circuit to charge the battery.

2 The 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 the second-order low-pass filter to obtain a stable sine wave output, which is then output to the Class C amplifier circuit composed of the transistor 13003 and its peripheral circuits to the coil and capacitor. The parallel resonant circuit radiates out. Provides energy to the receiving part.

The measured wire diameter of the air-core coupling coil of the parallel resonant circuit composed of the capacitor is 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 capacitance 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.