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`Qi Wireless Charging Standard
`- details and specifics about the Qi Wireless Charging Standard developed and
`promoted by the Wireless Power Consortium..
`
`Wireless Battery Charging Includes:
`Wireless charging basics Qi wireless charging A4WP wireless charging Buy the best wireless charger
`
`Qi, pronounced chee, has become the accepted standard for wireless charging.
`
`In order to provide interoperability, a key requirement for wireless charging, it was necessary to develop a standard
`that could be adopted by the major manufacturers. In this way the Qi charging standard enables one charger to be
`used for devices from many different manufactures and in this way become an accepted approach. If different
`chargers were required, this would require many different chargers for different devices and lead to confusion in the
`marketplace.
`
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`Accordingly the Qi wireless charging standard has become the accepted solution.
`
`The name Qi comes from Asian philosophy where it means "vital energy" which relates to wireless charging which
`can be seen as an intangible flow of power.
`
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`Wireless Power Consortium
`
`In order to be able to provide a standard for wireless battery charging technology, an industry group called the
`Wireless Power Consortium was set up.
`
`The Wireless Power Consortium held its first meeting in Hong Kong in December 2008. Since its inception its
`membership has grown from the eight initial companies to over 100.
`
`In August 2009, the Wireless Power Consortium published the Qi low power specification, and then just a month later
`the first product was certified.
`
`Under the auspices of the Wireless Power Consortium, the importance of wireless power has grown, with more
`companies taking the technology seriously. The first products using wireless power for their battery charging required
`the addition of an additional sleeve. However the first product with integrated Qi receivers for wireless battery
`charging were announced in March 2011.
`
`Qi wireless charging standard basics.
`
`The Qi standard has been developed by the Wireless Power Consortium and is applicable for electrical power
`transfer over distances of up to 40 millimetres (1.6 inches).
`
`The Qi wireless charging standard uses a power transmission pad that is akin to the charger that would be used in a
`normal wired system, and a compatible wireless power receiver that is located in the device to be charged. The
`power transfer then takes place using magnetic induction.
`
`The way in which the wireless power charging is achieved conforms to the standard and allows a single Qi wireless
`charger from any supplier to be used to charge any Qi compatible device. As most wireless charging systems now
`conform to this standard, it means that only one charger pad is required to charge all devices.
`
`There are two categories for Qi wireless chargers:
`
`Low power: The low power category covers chargers that can deliver power in the range 0 - 5 watts. This will
`cover most of the domestic portable devices like mobile phones, music players, Bluetooth earpieces, etc..
`
`Medium power: Chargers in the medium power category can deliver power up to 120 watts.
`
`Within any Qi wireless charging system, there are two main elements:
`
`Base Stations: The Qi base station is the device that provides inductive power for the wireless transmission. As
`such it contains a power transmitter of which a major element is the transmitting coil. The overall Qi charger
`typically has a flat surface. This is normally referred to as the Interface Surface. The mobile device or devices may
`be placed on top of this surface.
`
`Mobile Devices: The Qi mobile devices are those which consume the wirelessly transmitted power. This is
`typically used to charge the battery contained within the mobile device.
`
`To keep the efficiency as high as possible, it is necessary to ensure that he coupling between the transmit and
`receive coils is as high as possible. To achieve this the mobile device must be placed in the position where this can
`be achieved. The Qi standard defines two ways of achieving this:
`
`Guided positioning: This form of placement on a Qi charger involves the use of means to guide the user to
`place the mobile in the correct place on the Qi base station for charging.
`
`Placement anywhere: The second form of Qi charger placement does not require the user to accurately place
`the mobile device on a particular area of the charging surface. Instead a wider area is usable. This can be
`achieved by using more than one transmitter coil.
`
`The frequency used for Qi chargers is located between about 110 and 205 kHz for the low power Qi chargers up to 5
`watts and 80-300 kHz for the medium power Qi chargers.
`
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`Qi data protocol
`
`The Qi wireless power standard includes the capability for the base station and mobile device using a limited data
`transmission system. This enables the charge and base station to communicate to provide information about state of
`charge and the like. In this way, the mobile device can inform the base station when it is charged, etc.. In this way the
`base station can adapt its output to meet the needs of the mobile device and removing power transmission the mobile
`device is fully charged.
`
`In operation, initial detection occurs as a result of the deection of a change in capacitance or resonance of the
`transmitter coil. Once an object has been detected the base station validates the device placed on it for Qi charging
`compatibility. The base station sends an 8 bit data string. The receiving mobile device has to respond and provide the
`signal strength. The base station then sends multiple digital pings to provide information about the optimum
`positioning of the mobile device. Only when the device has been validated and the information been passed will
`charging commence. During the Qi charging process, the mobile device sends control data packets to adjust the
`power level and finally terminate charging.
`
`The Qi charger data communication protocol is defined to ensure that all devices can communicate properly.
`
`QI CAPABILITY
`Data speed
`
`Bit encoding
`
`Byte encoding
`
`Packet structure
`
`QI STANDARD DATA FORMAT
`DETAILS
`
`2 kbps
`
`Bi-phase
`
`Start bit; 8 bit data; parity bit; stop bit
`
`• Preamble (>=11 bit)
`• Header (1 Byte)
`• Message ( 1 to 27 Byte)
`One complete message per packet
` Payload for control
`• Checksum (1 Byte)
`
`Qi foreign object detection
`
`One of the issues that could arise with a wireless charging system is that a foreign metallic object is placed on or near
`the Qi charger. When this occurs, the charger can induce currents to flow in the object, dependent upon its placement
`and the magnetic coupling, and as a result the object can become exceedingly hot. This could present a danger,
`especially in a domestic environment.
`
`To prevent this occurring, the base station or charger is able to sense the presence of these objects and cut the
`charging action to ensure that only proper Qi mobile devices are coupled to the magnetic induction field and receive
`energy.
`
`Qi specification versions
`
`In order to meet the latest requirements, the Qi standard has been updated to cover new areas and to improve on
`others. The table below gives a summary of some of the highlights of the various Qi standard versions.
`
`QI VERSION
`
`QI STANDARD VERSIONS
`DETAILS
`
`• Qi transmitter power level 5 Watts.
`• Transmitter designs include: single coil transmitter, coil array transmitter, and moving coil transmitter.
`• Variety of Qi receivers
`• Limited flexibility in Qi transmitter designs
`
`• Increased Qi transmitter design flexibility: 12 different transmitter specifications available.
`• Improved "Foreign Object Detection". This is an important feature because it prevents heating of
`metal objects in the neighbourhood of an active transmitter.
`• Possibility of a Qi transmitter powered through a USB port.
`
`Version 1.0
`
`Version 1.1
`
`Issues with Qi
`
`Although the Qi standard has been the form of wireless charging that has become the preferred standard, it is not
`without its issues:
`
`Accurate alignment required: Correct alignment of the device under charge and the charger is required. Often
`users place items to be charged onto the charger, but find it has not charged because it has not been sufficiently
`accurately aligned. This is one of the complaints that many users have reported, but have become used to.
`
`Interference and EMI: Although devices can be made to operate within the requirements for EMI acceptance,
`this is not easy and also metal objects close to the charging coils can cause unusual effects with EMI. Also as the
`charge can have effects on close by objects.
`
`The Qi standard has become the only real wireless charging solution and ahs been incorporated in many new
`phones, especially top end ones. Chargers can be bought separately, and they are also found built into many new
`automobiles.
`
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