Wireless charging standard Qi. Wireless charging of smartphones based on Qi solutions

Qi is the Chinese word for "energy flow" (in English it is pronounced "chi") and the universal standard for wireless charging of devices powered by rechargeable batteries, such as players, cell phones and cameras.

Transmission of power is due to electromagnetic induction. In this case the receiver receives energy not through a traditional cable, but in a non-contact way, thanks to the use of electromagnetic fields. The principle is very simple: the transmitter Qi, which is a base station, sends the necessary energy to the receiver.

Description of the technology

The wireless charging standard Qi is based on the magnetic induction between the flat coils of the transmitting and receiving apparatus. The primary and secondary windings form two parts of a heartless resonant transformer. The charger circuit is shielded on the lower surface of the primary and upper secondary coil. This, as well as proximity, ensures an acceptable energy transfer efficiency. In addition, this minimizes the impact of the magnetic field on users.

Typically, the base station has a flat surface on which one or more mobile devices can be placed. This ensures that the vertical distance between the primary and secondary winding is small enough. In addition, there are two ways to align the windings horizontally.

In the first case, the user independently sets the secondary winding opposite the primary winding on the surface of the interface using the hints of the mobile device.

The second way, called free positioning, does not require active human participation. In one of the implementations, several primary windings are created for this purpose. Another option uses mechanical means to move the primary coil under the secondary.

Elements of construction

The power transmitter consists of two main functional units, namely the power conversion unit and the communication and control unit. The element of the first, generating a magnetic field, is the primary coil. The second changes the transmitted power to the level requested by the receiver. In addition, the base station may comprise more than one transmitter for serving multiple mobile devices, since one primary winding interacts with only one secondary at the same time. And, finally, the system unit provides electricity and controls the operation of several transmitters.

In the gadget there is a power receiving unit, which is a secondary winding, and a communication and control unit. The latter regulates the transmitted power to a level acceptable for the subsystem connected to the receiver's power output. An example of such a subsystem can serve as a rechargeable battery.

Stages of Communication

After activating the communication unit and controlling the transmitter, it sends a signal to the receiver to receive a response confirming the presence of the Q-compatible device.

After receiving the request, the receiver goes into the selection phase. If the proposed voltage is large enough, the pinging stage begins.

Upon receiving a response from the transmitter, the mobile device sends a signal strength packet and goes to the identification and configuration phase or sends a power transmission completion packet and remains in the ping phase.

Then an authentication package and management packets are sent. The receiver goes into the charging phase. At the same time, it controls the transmission of energy by transmitting base station control packets that contain information on the correction of the primary winding current, the energy received, the status of charging, and the completion of transmission.

What is the wireless charging point?

Qi-charging is universal because it provides compatibility of mobile phones and power adapters of various manufacturers. The only condition is that both the transmitter and receiver parts must conform to the Qi standard.

Thus, any wireless charger Qi will fit any mobile receiver Qi, regardless of brand and model. A lot of cell phones from different manufacturers, including Samsung, Nokia, LG, Sony, HTC and Motorola, already comply with the Qi standard and, therefore, can be connected to any charging station that meets its requirements. The number of compatible gadgets continues to grow, as the technology of wireless power transmission is supported by an increasing number of companies. Due to this, it is possible to charge the electronics powered by batteries with a single power source.

How it works?

Mobile charger is not the latest invention. In electric toothbrushes, inductive nutrition has been used for many years. In the process of wireless power transmission, a resonant inductive coupling is used between the transmitter of the base station and the receiver of the mobile phone. The primary coil constantly sends a test signal to the sender to check for a change in capacitance or resonance indicating the presence of a compatible phone. The transmitter modulates the charge and checks whether the wireless charging standard Qi is supported.

After compatibility and energy requirements are taken into account, the process of induction energy transfer begins. The contact between the receiver and the transmitter is maintained. Once the battery is fully charged, they will go into standby mode. Universal charging is activated and transmits power only if the connected gadget is on it.

Coils transmitting and receiving energy are specially shielded in order to reduce electromagnetic radiation.

Main features of the technology

• The method of contactless power transmission from a base station to a mobile device, which is based on the magnetic induction of the near field arising between the coils.
• Transmission about 5 watts of power using an appropriate secondary coil (having a typical external size of about 40 mm).
• Operation at frequencies from 100 to 205 kHz.
• Support for two methods of placement on the surface of the base station:
  • Directed positioning when the user is assisted in correctly positioning the mobile device in a location providing power at one or more fixed points;
  • Random placement on the surface of the charging station.
• A simple communication protocol that allows a phone or a tablet to guide the process.
• Significant design flexibility for integrating the system into a mobile device.
• Low level of energy consumption in standby mode (depending on the implementation).

One for all

How convenient would it be to have one Qi-charger for all phones, players, cameras without a lot of confusing cables?

While countless new smartphones cover the world, the battery life is getting shorter. And every manufacturer and even every gadget has its own charger. And with each purchase their number increases. In the end, the user is lost in a heap of various power adapters. Thanks to Q-technology, they become unnecessary, and tangled bundles of cables disappear, and this is not all the advantages of this technology.

Just as Wi-Fi became the world standard for wireless Internet connections, and Bluetooth eliminated the need to hold the phone in hand, so Qi becomes the world standard for inductive charging of gadgets on batteries.

Is electromagnetic radiation harmful?

The opinions of the experts were divided. On the one hand, many scientists confirm that a small amount of electromagnetic radiation does not cause harm to wireless charging. Others talk about the great danger to which the human body is exposed.

So how much electromagnetic energy is emitted by the Qi system? Very little. The Qi principle has been used in electric toothbrushes for many years without affecting human health. The circuit of the charger is such that, due to its small area of operation, electromagnetic radiation is extremely limited. It exists only in the immediate vicinity of the wireless transmitting station and only when the gadget is on it. Electromagnetic radiation is reduced even further by additional shielding in the transmitting and receiving coils.

Wireless Power Consortium

Wireless Power Consortium (WPC) was founded on December 17, 2008. At the same time, a unified program for the development of this technology was approved.

The wireless charging standard Qi ensures its versatility for all Qi-compatible electronic gadgets. This means that each device compatible with it can be charged on any Qi-compatible station. The WPS includes 250 members, including market leaders Samsung, Nokia, LG, Panasonic, HTC, Sony, Microsoft and Motorola, making it the largest association of manufacturers that support wireless types of chargers.

According to the chairman of WPC Menno Treffers, due to the increase in the number of products using Qi, it is important to be sure that every mobile charger works correctly with all supported Qi gadgets. This is facilitated by the constantly updated database, created by Testronic, which makes it easy to determine whether a new product will be compatible with previously certified products. The wireless charging standard Qi has become one of the most important technical developments for users of phones and tablets, which are now used daily in work and life.