Main standards for wireless charging ：Qi and Airfuel

Wireless charging, also known as inductive charging and non-contact inductive charging, uses near-field induction what's also called inductive coupling and the power supply equipment (charger) transfers energy to a device that uses electricity.

The device uses the received energy to the battery charging and used for its own operation at the same time. Basically, because the charger and the electric device transfer energy through inductive coupling, there is no need to use wires to connect between the two, so both the charger and the electric device can achieve no conductive contacts exposed. This is more convenient than wired charging.

Main standards for wireless charging

Wireless charging standards mainly include: Qi standard, AirFuel (AirFuel Alliance).

Qi standard

The Qi standard was first published in 2010, and it described an inductive method for wirelessly charging devices. In addition to specifying three different power ranges for wireless chargers, it laid out the way that devices would communicate with charging stations to ensure safe and efficient charging.

Qi is a short-distance low-power wireless inductive power transmission interconnection standard formulated by the Wireless Power Consortium WPC. Its main purpose is to provide convenient and universal wireless charging for mobile phones and other portable electronic devices.

Under the Qi standard, the low-power standard uses inductors to transmit power of 5W or less, and both transmit and receive use flat inductors to transmit energy in an inductive coupling mode. The distance between two inductors (coils) can reach 5mm, which can also be changed to 40mm according to needs.

The output voltage can be stabilized at a specific value. The method is to notify the input terminal to increase or decrease the power through digital communication at the output terminal to achieve the effect of stabilizing the voltage. Digital communication is one-way (only the signal is sent from the power output terminal to the power input terminal), and the information is sent by backscatter modulation. Which is changing the load at the output terminal changes the current of it, thereby changing the current of the input coil.

According to the current change of the inductance of the input terminal, the required control signal can be obtained by demodulating. In this way, the input terminal can regulate the input power according to the control signal to stabilize the voltage at the output terminal.

AirFuel Alliance：

The AirFuel Wireless Charging Alliance was formed by the merger of Wireless Power (A4WP) and Power Matters Alliance (PMA) in 2015. It is committed to integrating magnetic resonance and magnetic induction technologies to promote a unified wireless charging standard. AirFuel technology includes resonance (Resonant), radio frequency charging (RF). AirFuel's resonance technology can charge multiple devices at the same time, with a maximum charging height of up to 5 cm. AirFuel radio frequency technology can carry out low-power charging in the range of a few centimeters to one meter. Therefore, AirFuel technology has relatively greater freedom in the charging space, but it also has greater radiation problems.

Advantage of Qi

Qi’s advantages are mainly reflected in versatility.

Almost the world’s major mobile phone manufacturers have included the Qi standard launched by the WPC, the world’s first standardization organization. Including Samsung, Apple, Huawei, OPPO, Xiaomi, vivo, Nokia, etc. This means that these manufacturers Wireless chargers between the two can be compatible, and chargers of different brands can wirelessly charge other mobile phones.

In addition, the forms of products that are included in the Qi standard are becoming more abundant, including watches, notebooks, headphones, etc. The Qi standard is currently the most mainstream electromagnetic induction technology in the world, and it is also the most widely used standard worldwide, with a coverage rate of up to 90%. The Qi standard is divided into 4 versions. Supports wireless charging up to 30W.

version	Maximum power
1.0	5W	The charging line can be single coil, array coil or moving coil
1.1	5W	Added 12 charger specifications and added foreign body detection
1.2	Baseline Power Profile(BPP):5W Extended Power Profile(EPP):15W	The maximum power is increased to 15W, the thermal test of the charger is improved, also the timing specification and the sensitivity of foreign body detection.
1.2.3	EPP Power Class 0:5W-30W	Added Power Class 0, allowing the product to negotiate up to 30W power with the charger
1.2.4	-	Improve test requirements to make it easier to obtain EPP test