Qi is the Chinese word for “energy flow” (pronounced “chi” in English) and the universal standard for wireless charging of battery-powered devices such as players, cell phones and cameras.
Power transmission occurs due to electromagnetic induction. In this case, the receiver does not receive energy through a traditional cable, but in a non-contact way, thanks to the use of electromagnetic fields. The principle is very simple: the Qi transmitter, which is the base station, directs the necessary energy to the receiver.
Technology description
The Qi wireless charging standard is based on magnetic induction between the flat coils of the transmitter and receiver. The primary and secondary windings form two parts of a coreless resonant transformer. The charger circuit is shielded on the lower surface of the primary and upper - secondary coils. This, as well as its proximity guarantee an acceptable energy transfer efficiency. In addition, this minimizes the effect of the magnetic field on users.
Typically, a 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 windings is sufficiently small. 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 on the interface surface using the prompts of the mobile device.
The second method, called free positioning, does not require the active participation of a person. In one of the implementations, several primary windings are created for this. Another option uses mechanical means to move the primary coil under the secondary.
Structural elements
The power transmitter consists of two main functional blocks, namely, a power conversion unit and a communication and control unit. The element of the first, generating a magnetic field, is a primary coil. The second changes the transmitted power to the level requested by the receiver. In addition, the base station may contain more than one transmitter for serving several mobile devices, since one primary winding at the same time interacts with only one secondary. And finally, the system unit provides electricity and controls the operation of several transmitters.
The gadget contains 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 power output of the receiver. An example of such a subsystem is a battery.
Stages of communication
After activating the communication and control unit of the transmitter, it sends a signal to the receiver to receive a response confirming the presence of a Q-compatible device.
Upon receipt of the request, the receiver enters the selection phase. If the proposed voltage is large enough, then the pinging stage begins.
Upon receipt of a response from the transmitter, the mobile device sends a signal strength packet and enters the identification and configuration phase or sends an energy transmission completion packet and remains in the ping phase.
Then an identification packet and control packets are sent. The receiver enters the charging phase. At the same time, it controls the transfer of energy by transmitting control packets to the base station, which contain information about adjusting the primary winding current, about the received energy, about the charging status, and about the completion of the transfer.
What is a wireless charging point?
Qi-charging is universal because it provides compatibility between mobile phones and power adapters from different manufacturers. The only condition is that both parts — transmitter and receiver — must comply with the Qi standard.
Thus, any Qi wireless charger will fit any Qi mobile receiver, regardless of make or model. Many 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 wireless power transmission technology is supported by an increasing number of companies. Thanks to this, you can charge the electronics that are running on batteries with a single power source.
How it works?
A mobile charger is not the latest invention. Inductive power has been used in electric toothbrushes for many years. In the process of wireless power transmission , 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 changes in capacitance or resonance, indicating the presence of a compatible phone. The transmitter modulates the charge and checks if the Qi wireless charging standard is supported.
Once the compatibility and need for energy are taken into account, the process of induction transfer of energy begins. In this case, 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 transfers energy only if the plug-in gadget is on it.
Coils transmitting and receiving energy are specially shielded in order to reduce electromagnetic radiation.
Technology Highlights
- A method of contactless power transfer from a base station to a mobile device, which is based on near-field magnetic induction arising between the coils.
- Transfer about 5 watts of power using an appropriate secondary coil (having a typical external size of about 40 mm).
- Work at frequencies from 100 to 205 kHz.
- Support for two methods of placement on the surface of the base station:
- guided positioning, when the user is helped to correctly position the mobile device in a place that provides power through one or more fixed points;
- arbitrary placement on the surface of the charging station.
- A simple communication protocol that allows a phone or tablet to manage the process.
- Significant design flexibility for integrating the system into a mobile device.
- Low standby power consumption (depending on 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?
As countless new smartphones span the world, battery life is getting shorter. And every manufacturer and even every gadget has its own charger. And with each purchase their number increases. Ultimately, the user gets lost in a bunch of various power adapters. Thanks to Q-technology, they become unnecessary, and tangled tangles of cables disappear, and this is not all the advantages of this technology.
Just as Wi-Fi has become the world standard for wireless Internet connections, and Bluetooth has eliminated the need to hold the phone in hand, Qi is becoming the world standard for inductive charging of gadgets on batteries.
Is electromagnetic radiation harmful?
The opinions of experts were divided. On the one hand, many scientists confirm that a small amount of electromagnetic radiation from wireless charging does no harm. Others speak of 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 people's health. The circuit of the charger is such that due to the small area of its action, 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 further reduced 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 Qi Wireless Charging Standard provides its versatility for all Qi-compatible electronic gadgets. This means that every device compatible with it can be charged at 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 supporting wireless types of chargers.
According to WPC chairman Menno Treffers, in connection with the increase in the number of products using Qi, it is important to be sure that each 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 the new product will be compatible with previously certified products. The Qi wireless charging standard has become one of the most important technical developments for users of phones and tablets, which are now used daily in work and life.