Research And Design Of Inductively Coupled Wireless Power Transfer System And Its Key Circuits

In recent years,the emergence of wireless power transfer technology has effectively solved the binding of cables of different specifications between various electrical equipment,and made the power consumption more flexible and safe,so it has gained wide attention from all walks of life.With the maturity of related technologies,wireless power transfer technology has been applied in many scenarios.Among them,inductively coupled wireless power transfer technology(Inductively Coupled Power Transfer,ICPT)is the most widely used and mature.In the wireless power transfer system,the wireless power transmitting function can be realized by adopting the general MCU(Microcontroller Unit,MCU)solution.However,using the general MCU solution requires adding more peripheral circuits,which increases the complexity of production testing,and it is not conducive to ensuring product consistency,and makes the product development cycle longer.In this paper,a system-ona-chip(SOC)method is used to design a main control circuit of the transmitter,which greatly integrates the peripheral circuit into the chip,making the external circuit simple,increasing product reliability,and reducing product development cycle and difficulty.In the wireless power receiver system,in order to enable the receiver to be applied to smaller and more integrated terminal products,the receiver circuit integrates the power parts such as synchronous rectification circuit,output control circuit and other control circuits.At the same time,the rectifier circuit and output circuit are optimized to improve the overall efficiency.During the research and design process,I mainly carried out the following work:1)A wireless power transmitter circuit that complies with Qi specifications is designed.The Tx chip integrates digital demodulation and decoding circuit,pulse width modulation(PWM)output module,high-precision oscillator(OSC),rail-to-rail operational amplifier,current sense amplifier,12-bit high precision successive approximation register analogto-digital Converter(SAR-ADC),etc.The circuit of different modules has been optimized to ensure that its performance meets the requirements of the Tx main control chip.2)The overall system design and testing of the wireless power transmitter are carried out.Designed the hardware and software of the transmitter system,and designed the Q value detection and foreign object dected(FOD)functions.For the Q value detection,a method for calculating the positive and negative cycles of free oscillation is proposed.The oscillating signal is converted into a periodic signal through a comparator,and then the IO port of Tx chip can be counted.Finally,the system has been tested and analyzed.The designed Tx chip and system have good performance and meet the Qi standard requirements.Using IDT(Integrated DNA Technologies,IDT)receiver for testing,the system efficiency can reach up to 88% at 12 V output.Q-value detection has high sensitivity,and FOD test also meets Qi standard requirements.3)A wireless power receiver circuit that meets the Qi specification was designed,and the chip was tape out and verification.The key circuit modules of the receiver are designed,such as the synchronous rectification module,the output control circuit module,the system power generation circuit,the voltage comparator,the drive circuit,etc.Among them,in the synchronous rectifier circuit,in order to improve the rectification efficiency and performance,a method of using digital pulses to control the effective width of the rectification is proposed to compensate for the turn-off delay caused by circuits such as comparators,logic circuits and drive circuits so as to realize the pre-shutdown effect of the synchronous rectifier MOS to prevent the occurrence of reverse leakage current.From the results of system test waveforms,the designed digital pulse width control method can effectively achieve the pre-shutdown function of the rectifier MOS.And from the efficiency test results,when the output voltage is 5V,the maximum efficiency with early shutdown function is higher 8% than that without shutdown function,the maximum system efficiency at 5V,9V and 12 V output are 82%,83.8% and 88%,respectively.4)In the output control strategy part of the receiver circuit,in order to enable the output of the receiver to directly charge the battery,a multi-mode battery charge management circuit is designed.By controlling the effect of different feedback loops,constant current,constant voltage output and other protection functions can be achieved,so that both constant voltage output and direct battery charging can be achieved.In order to improve the overall efficiency when charging the battery,an adaptive rectified voltage control method is proposed in the control method.In the system test,the supercapacitor analog battery was used for charging test.The test waveforms showed that the designed circuit meets the battery charging management requirements.When the constant current is charged to 4V,the system efficiency reaches 78.3%.