Wireless Charging Circuit System Based On SP+BUCK Load Amplification

Wireless charging technology, also called generic wireless power transmission, the principle is similar to a transformer, the transmitter circuit produces an alternating current through the primary coil, which will induce an alternating electromagnetic field in the primary coil,the secondary coil produce induced current by receiving the alternating electromagnetic field, and to achieve transfer of energy by electromagnetic induction.However, the transmission path is the air, which makes the coupling degree between the wireless charging coil is much lower than that of the transformer, which is the most important bottleneck of the wireless charging coil.At this stage, the main method to overcome the low coupling degree in the transmission coil and the receiving coil is to connect a resonant capacitor to improve the distance and efficiency of wireless transmission.Because the main wireless charging technology is the energy transfer through the electromagnetic wave, there are many factors that affect the efficiency of wireless charging,but no matter what kind of wireless charging circuit topology, the efficiency of the high and low frequency, coil coupling, load, the size of the required energy is the main factor, but at this stage there is no good theoretical model to explain the wireless charging parameters.At present, the mainstream of the wireless charging industry is the QI standard of the WPC alliance.QI standard is the world’s first wireless charging standardization organization, the standard is the most widely used in all standards, the most widely used in the market and the main products are based on the QI standard.The operating frequency range of QI standard is between 110 Khz and 205 Khz, the transmitter and receiver of the standard are two series resonant circuits which are in the same resonant frequency.The standard technology of the wireless transmission distance once morethan 5mm, transmission efficiency will be a very sharp drop,At the same time in the transmission range of 5mm within the range of transmission power less than 2W transmission efficiency will also be a sharp decline.These two major limitations of the technology are mainly used in power 2W to 5W and transmission distance is less than5 mm.In this paper, the problem of the wireless charging circuit is presented, and a kind of SP+BUCK circuit topology is proposed. This structure is a kind of circuit topology which can effectively improve the transmission distance and low power transmission efficiency. The structure of the BUCK circuit is used to enlarge the impedance of the SP circuit, which greatly improves the load resistance of the circuit, which greatly improves the reflection impedance of the receiving end. If the topology used in Qi, in the transmission power less than 2W, transmission distance is less than 5mm, the average transmission efficiency of the system can maintained at more than 70%,The transmission efficiency is about 60% when the transmission distance is 20 mm,The transmission efficiency is about 50% when the transmission distance is 30 mm,and with the transmission distance becomes shorter and improve. This structure greatly improves the problem of low transmission distance and low power efficiency under the traditional QI protocol. This circuit topology is particularly suitable for applications where a certain transmission distance is required and the load current is not high.