A complete wireless charging system includes TX terminal and Rx terminal. The structure of wireless charging is similar to an air core transformer, and the energy transmission is realized by coil coupling. Usually, the transmitting coil and its driving circuit are installed in a charging board, and the receiving coil and its driving circuit are embedded in the equipment to be charged, such as smart phones. The efficiency of energy transmission is related to the distance between coils, the degree of coil alignment, coil direction, coil material, magnetic field shielding, impedance matching, emission frequency and duty cycle. Among them, the distance and alignment between coils have a great impact on the transmission efficiency.
Circuit principle:Three transmitting coil arrays are used to expand the charging area in order to obtain better charging efficiency and experience. Bq500410a enables three transmitting coils in turn at a time interval of 400 ms, and enables the analog switch of the corresponding comm feedback signal path at the same time. Bq500410a will look for the strongest comm feedback signal, and then drive the corresponding transmitting coil to obtain the best coil matching. Therefore, at the same time, only one transmitting coil is working, and the other two transmitting coils are in standby mode. In order to reduce electromagnetic radiation, the wireless charging system also adds a ferrite magnetic separator on the back of the coils at both ends of the transceiver, so that the energy transmission area is limited between the two magnetic separators, so as to avoid the interference of radiation generated by the wireless charging system on smart phones or other devices.
The low power consumption of the system is realized by adding MSP430 low power MCU of Ti and bq500410a. In order to achieve low power consumption, one of the most direct methods is to directly turn off the power supply when there is no load to completely shut down the bq50041a. However, if this is done, the information including charge state, error state, operation mode and drive pin state will be completely lost. After adding MSP430, bq500410a can be shut down periodically to save power consumption, and its wake-up signal is provided by MSP430. At the same time, various status information is also saved by MSP430, and the LED status indicator is also driven by MSP430 instead of bq500410a. In this way, although the complexity and cost of the system are improved, the standby power consumption is reduced from 300 MW to about 90 MW.
Comments and analysis of technical editor of electronic enthusiast network:
The proposed wireless charging system solves the problem of small charging area in the traditional single coil scheme, and greatly improves the user experience. Therefore, the scheme of this paper has higher market value. In addition, the low-power circuit added in this paper can reduce the standby power consumption from 300 MW to 90 MW, which can better meet the needs of some low-power devices.