Principle, function and structure of wireless charging coil

The wireless charging system first selects the principle of electromagnetic induction, and ends the energy transmission through the intermittent energy coupling of the coil. When the system is working, the input end converts AC mains into DC power through a full-bridge rectifier circuit, or directly supplies power to the system with 24V DC power. After the output DC power passes through the power processing module, it is converted into high-frequency AC power through the 2M active crystal oscillator inversion and supplied to the primary winding. Through the coupling energy of the two induction coils, the receiving conversion circuit converts the current output by the secondary coil into direct current to charge the battery.

The square wave output from the active crystal oscillator of the wireless charger coil is filtered by a second-order low-pass filter to obtain a stable sine wave output. , and radiate in to provide energy for the receiving part. The air-core coupling coil of the parallel resonant circuit composed of capacitors has a wire diameter of 0.5 mm, a diameter of 7 cm, an inductance of 47 uH, and a carrier frequency of 2 MHz. According to the parallel resonance formula, the matching capacitance C is about 140 pF. Therefore, the transmitting part selects the power carrier frequency that is attacked by the 2MHz active crystal oscillator close to the resonant frequency.

At that time, the first choice for intermittent charging of mobile phones, MP3s, and notebook computers was the traditional charging method of connecting one end of the AC power source and the other end to the rechargeable battery of the portable electronic device. There is a lot of bad luck with this approach. First, repeated insertion and removal will only damage the joint. Others also present a risk of electric shock. Therefore, the non-contact inductive charger was born at the end of the last century, and quickly attracted attention from all walks of life with its advantages of convenience, low cost, and no wiring. Therefore, wireless charging, high energy transmission efficiency, and portability have become one of the research directions of charging systems.

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