Technology Analysis of Magnetic Resonance Wireless Charging Circuit

At present, the most common standards in the field of wireless charging are (QI) wireless charging standards in electromagnetic induction techniques. The wireless charging system using QI standard is mainly based on electromagnetic induction, and the electromagnetic induction coupling frequency used is 100 kHz to 300 kHz. This system can only charge a single device, and the device is placed in a specific direction and keeps very close to the charger. As the application of wireless power transmission is increasingly concerned with the application of wireless power transmission, it is necessary to make full use of the power conversion designer of the resonant coupling advantage to start the target steering magnetic resonance Class D and the E class inverter topology. . These topologies are not new inventions, which have been successfully applied in RF (RF) applications, and the term "amplifier" is widely used. The main advantages of these topologies used in the transmitter portion of the wireless charging system (shown in Figure 1) are high efficiency at the operating frequency within 1-10 MHz range. Air FuEL Alliance (established in 2015) This method of using 6.78 MH frequency switching in ISM (Industrial-Science-Medical) band, wherein the high Q coefficient resonator can use a weaker magnetic field in the peripheral region to be performed in a larger distance. Power transmission to charge for multiple devices placed in any direction. The law of Faranda pointed out that when the magnetic flux in the coil changes, the induced electromotive force is generated. In the wireless power transmission, the RF power amplifier drives the power transmitting unit (PTU) composed of the coil in the tuning circuit to produce a changed magnetic flux. The power receiving unit (PRU) consisting of a coil tuning to the same frequency is transversely cut, thereby generating a voltage. This voltage depends on the change in magnetic flux and the number of turns. The output from the receiving coil is rectified and converted into the level required for the portable device. The coupling depends on the tightness of the two coils, is defined by the coupling coefficient k. K in less than 0.5 represents the loose coupling system used by magnetic resonance coupling. Figure 1 shows the system block of the PTU and PRUs. A microcontroller with Bluetooth communication function (according to the AIRFuel standard, can also be communicated) for requesting and adjusting the amount of power required to be charged by the charging device.

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