In order to enable different brands of products to share the same charger and improve the versatility of wireless chargers, the world's first standardization organization to promote wireless charging technology - Wireless Power Consortium (hereinafter referred to as the "Alliance") launched the "wireless charging" standard, under the Wireless Power Alliance (WPC) standard, the power consumption of wireless transmission is only 0~5W. Systems that reach this standard range use inductive coupling between 2 planar coils to transfer power from the power transmitter to the power receiver. The distance between the primary and secondary coils is typically 5mm, and the output voltage regulation is handled by a global digital control loop, where the power receiver communicates with the power transmitter and generates power dissipation. This communication is a one-way communication from the power receiver to the power transmitter through backscatter modulation. In backscatter modulation, the power receiver adjusts the load, which changes the current consumption of the power transmitter. These current changes are monitored and demodulated into the information required for the two devices to work together. Communication protocols include analog, digital acoustic pulses (ping), identification, configuration, and power transmission.
The typical boot sequence that occurs when a power receiver is placed on a power transmitter is as follows:
(1) An analog ping from the power transmitter detects the presence of an object.
(2) The digital ping from the power transmitter is an extended version of the analog ping and gives the power receiver time to reply to a signal strength packet. If the signal strength pack is valid, the power transmitter keeps the coil energized and proceeds to the next step.
(3) In the identification and configuration phase, the power receiver will send some data packets, identify them, and provide configuration and setting information to the power transmitter.
(4) In the power transmission stage, the power receiver sends a control error packet to the power transmitter to increase or decrease the power. Control error packets are sent approximately every 250ms during normal operation and every 32ms during large signal changes. In addition, during normal operation, the power transmitter sends power packets every 5 seconds.
(5) In order to terminate the power transmission, the power receiver sends a "stop charging" message or does not communicate within 1.25s, so that the power transmitter enters a low-power state. Under the Qi standard, mobile phones, cameras, computers and other products can be charged with Qi wireless chargers, and large-scale wireless charging will be possible.
