Shenzhen Waweis Technology Co., Ltd.

Home> News> Introduction to Qi standard and wireless charging solution
May 12, 2020

Introduction to Qi standard and wireless charging solution

Wireless charging technology shows great market potential in the consumer market. Charging electronic devices without wires not only provides a convenient solution for users of portable devices, but also allows designers to find more innovative solutions to problems. Many battery-powered portable devices, from mobile phones to electric cars, could benefit from the technology.

Inductive coupling method can realize efficient and universal wireless charging. To make it easy to use and to benefit both designers and consumers, the wireless charging alliance (WPC) has developed a standard that creates interoperability between the Power Supply (wireless transmitter, charging station) and the power supply (wireless receiver, portable device). WPC was founded in 2008 and consists of companies in various industries in Asia, Europe and the United States, including electronic equipment manufacturers and original equipment manufacturers (oems). The WPC standard defines the types of inductive coupling (coil construction) and the communication protocols used for low-power wireless devices. Any device working under this standard can be paired with any other wpc-compatible device. An important advantage of this approach is that it USES these coils to communicate between the wireless transmitter and the wireless receiver. For a typical application diagram, see figure 1

WPC standard for wireless charging
Under WPC standard, the "low power" of wireless transmission means the power consumption is only 0 ~ 5W. Systems that reach this standard range use inductive coupling between two planar coils to transmit power from a wireless transmitter to a wireless receiver. The distance between the two coils is generally 5mm. The output voltage is regulated by a global digital control loop, in which the wireless receiver communicates with the wireless transmitter and requires more or less power. The communication is a one-way communication from the wireless receiver to the wireless transmitter through backscatter modulation. In backscatter modulation, the wireless receiver coil is loaded and the current consumption of the wireless transmitter is changed. We monitor these current changes and demodulate them to the information needed for the two devices to work together.

The WPC standard defines three main aspects of the system -- the wireless transmitter that provides the power, the wireless receiver that USES the power, and the communication protocol between the two devices. Below, we will introduce these three aspects in detail.


Fig. 1 functional structure diagram of the transmitter of a typical zhuo chip micro wireless charging terminal

1554660133285935

Wireless transmitter

The direction of power transmission is always from the wireless transmitter to the wireless receiver. The key circuit of the wireless transmitter is the primary coil used to transmit power to the wireless receiver, the control unit that drives the primary coil, and the communication circuit that demodulates the voltage or current of the primary coil. We limited the flexibility of the wireless transmitter design to provide consistent power and voltage levels to the wireless receiver.

The wireless receiver ACTS as a compatible device for the wireless sender and also provides configuration information. Once the transmitter starts transmitting power, the wireless receiver sends error packets to the wireless transmitter, requiring more or less power. Once a "power cut" message is received, or if the packet is not received for more than 1.25 seconds, the wireless transmitter stops supplying power. When there is no power transmission, the wireless transmitter goes into low-power standby mode.

The WPC specification allows the use of fixed and mobile configurations. A single fixed coil (called type A1) is a solution supported by micro wireless charging on a chip.

The wireless transmitter, which is usually a flat user on which the wireless receiver is placed, is connected to the power supply. The WPC compliant device coil ACTS as a 50% duty cycle resonant half bridge with an input of 19VDC (± 1v). If the wireless receiver requires more or less power, the coil frequency will vary, but will remain between 110 and 205kHz, depending on the power demand.


Wireless receiver
The wireless receiver is usually a portable device. The key circuit of the wireless receiver is the secondary coil used to receive power from the wireless transmitter, the rectifying circuit used to convert AC to DC, the power regulating circuit used to convert a non-stabilized DC to a stabilized DC, and the communication circuit used to modulate the signal to the secondary coil. The wireless receiver is responsible for all communication of its identity and power requirements, because the wireless transmitter is just a "listener."

Communication protocol
The communication protocol includes analog and digital sound pulses (pinging); Identification and configuration and power transmission. The typical startup sequence when the wireless receiver is placed above the wireless transmitter is as follows:

The simulated ping from the wireless transmitter detects the presence of the object

The digital ping from the wireless sender is an extended version of the analog ping and gives the wireless receiver time to reply to a signal strength packet. If the message strength packet is valid, the wireless transmitter will keep the coil energized and proceed to the next step

During the identification and configuration phase, the wireless receiver will send some packets to identify them and provide configuration and setup information to the wireless transmitter

In the power transmission phase, the wireless receiver sends control error packets to the wireless transmitter to increase or decrease power. These packets are sent every about 250ms during normal operation and every 32ms during large signal changes. In addition, during normal operation, the wireless transmitter will send power packets every five seconds.

To terminate the transmission, the wireless receiver either sends a "stop charging" message or does not communicate for 1.25 seconds. Either of these events will put the wireless transmitter into a low-power, power-saving state.
Although we limited the design of the wireless transmitter in order to make it compliant with the WPC standard, there was more freedom in designing the wireless receiver. We can adjust the coil size of the wireless receiver to meet the size requirement of the equipment. With the typical efficiency of 70% of the output of 5V and 500mA, we conduct full-wave rectification of the coil voltage at the wireless receiver. Because the communication between the two devices is one-way, the WPC chooses the wireless receiver as the "narrator." Inductive power transmission works by coupling the magnetic field once to the secondary coil. The uncoupled magnetic force line rotates around the coil once, and as long as the magnetic force line is uncoupled with the parasitic load, there will be no loss (e.g., eddy loss of metal, etc.).

WPC solution for zhuoxi micro wireless charging
Zhuoxi micro USES a variety of newly developed IC such as frequency modulation, fixed frequency voltage regulation and duty cycle adjustment to provide a reliable solution for wireless transmitter at the same time. The wireless transmitter USES ZXW8021, ZXW 8022, ZXW8023, ZXW8024 and other devices. The wireless transmitter is based on the ZXW802X series, which supports the A11(mp-a11) type (single coil) structure. Receiver and transmitter IC are common to other wpc-compatible solutions.

The wireless transmitter solution is implemented through ZXW802X. The device demodulates and decodes serial data from a wireless receiver. The control circuit first confirms that the wireless receiver is actually a wpc-compatible device, and then the wireless transmitter is configured accordingly.

conclusion
The WPC standard is a set of guidelines that allow manufacturers to believe that their components can work in concert with other WPC certified components designed for inductive power transmission to develop a wide range of solutions.


Best Regards,

Ada Zheng


Share to:

LET'S GET IN TOUCH

We will contact you immediately

Fill in more information so that we can get in touch with you faster

Privacy statement: Your privacy is very important to Us. Our company promises not to disclose your personal information to any external company with out your explicit permission.

Send