Qi (standard)
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Qi (pronounced ; from the
Chinese Chinese can refer to: * Something related to China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the List of countries and dependencies by population, world's most populous country, with a populat ...
word
qi
qi
;
traditional Chinese Traditional Chinese characters are one type of standard Chinese character Chinese characters, also called ''hanzi'' (), are logogram In a written language A written language is the representation of a spoken or gestural la ...
: 氣) is an
open Open or OPEN may refer to: Music * Open (band) Open is a band. Background Drummer Pete Neville has been involved in the Sydney/Australian music scene for a number of years. He has recently completed a Masters in screen music at the Australia ...
interface standard In telecommunication Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both its essence and the nature of ...
that defines
wireless power transfer Wireless power transfer (WPT), wireless power transmission, wireless energy transmission (WET), or electromagnetic Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that o ...
using
inductive charging Inductive charging (also known as wireless charging or cordless charging) is a type of wireless power transfer. It uses electromagnetic induction to provide electricity to portable devices. Inductive charging is also used in vehicles, power to ...

inductive charging
over distances of up to 4 cm (1.6 inches), developed by the
Wireless Power Consortium The Wireless Power Consortium (WPC) is a multinational technology Technology ("science of craft", from Ancient Greek, Greek , ''techne'', "art, skill, cunning of hand"; and , ''wikt:-logia, -logia'') is the sum of Art techniques and material ...
. The system uses a charging pad and a compatible device, which is placed on top of the pad, charging via
resonant inductive coupling upright=1.7, Diagram of the "WiTricity" resonant inductive wireless power system demonstrated by Marin Soljačić's MIT team in 2007. The resonant circuits were coils of copper wire which resonated with their internal capacitance (dotted capacitor ...
. As of February 2020 the almost 500 mobile device manufacturers working with the standard include
Apple An apple is an edible fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this fie ...
, Asus,
Google Google LLC is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational stat ...

Google
,
Huawei Huawei Technologies Co., Ltd. ( ; ) is a Chinese multinational corporation, multinational technology company, technology corporation headquartered in Shenzhen, Guangdong, China. It designs, develops and sells telecommunications equipment, cons ...
,
LG Electronics LG Electronics Inc. () is a South Korean Multinational corporation, multinational electronics company headquartered in Yeouido-dong, Seoul, South Korea. LG Electronics is a part of the LG Corporation, the fourth-largest ''chaebol'' in South K ...

LG Electronics
,
Samsung The Samsung Group (or simply Samsung) ( ko, 삼성) is a South Korean Multinational corporation, multinational manufacturing Conglomerate (company), conglomerate headquartered in Samsung Town, Seoul, South Korea. It comprises numerous affil ...
,
Xiaomi Xiaomi Corporation (; ), registered in Asia as Xiaomi Inc., is a Chinese designer and manufacturer of consumer electronics Consumer electronics or home electronics are electronic Electronic may refer to: *Electronics Electronics ...

Xiaomi
, and
Sony , commonly known as Sony and stylized as SONY, is a Japanese multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from mult ...

Sony
. First released in 2008, the Qi standard has been incorporated into more than 200 smartphones, tablets and other devices by 2017.


Design

left, Fig. 1-1 Devices that operate with the Qi standard rely on
electromagnetic induction Electromagnetic or magnetic induction is the production of an electromotive force In electromagnetism Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs b ...

electromagnetic induction
between planar coils. A Qi system consists of two types of devices – the Base Station, which is connected to a power source and provides inductive power, and Mobile Devices, which consume inductive power. The Base Station contains a power transmitter that comprises a transmitting coil that generates an oscillating
magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. For instance, a vector field in the plane can be visualised as a collection of arrows with ...

magnetic field
; the Mobile Device contains a power receiver holding a receiving coil. The magnetic field induces an
alternating current Alternating current (AC) is an electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'natu ...
in the receiving coil by
Faraday's law of induction Faraday's law of induction (briefly, Faraday's law) is a basic law of electromagnetism Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electric c ...
. Close spacing of the two coils, as well as shielding on their surfaces, ensure the inductive power transfer is efficient. Base Stations typically have a flat surface—referred to as the Interface Surface—on top of which a user can place one or more Mobile Devices. There are two methods for aligning the transmitting coil (part of the Base Station) and receiving coil (part of the Mobile Device) in order for a power transfer to happen. In the first concept—called guided positioning—a user must place the Mobile Device on a certain location of the Base Station's surface. For this purpose, the Mobile Device provides an alignment aid that is appropriate to its size, shape and function. The second concept—referred to as free positioning—does not require the user to place the Mobile Device in direct alignment with the transmitting coil. There are several ways to achieve free positioning. In one example a bundle of transmitting coils is used to generate a magnetic field at the location of the receiving coil only. Another example uses mechanical means to move a single transmitting coil underneath the receiving coil. A third option is to use a technique called "Multiple Cooperative Flux Generators." Figure 1-1 illustrates the basic system configuration. As shown, a power transmitter includes two main functional units—a power conversion unit and a communications and control unit. The diagram shows the transmitting coil (array) generating the magnetic field as part of the power conversion unit. The control and communications unit regulates the transferred power to the level that the power receiver requests. The diagram also demonstrates that a Base Station may contain numerous transmitters, allowing for multiple Mobile Devices to be placed on the same Base Station and inductively charge until each of its batteries are fully charged. Finally, the system unit in the diagram comprises all other functionality of the Base Station, such as input power provisioning, control of multiple power transmitters, and user interfacing. A power receiver comprises a power pick-up unit, as well as a communications and control unit. Similar to the power conversion unit of the transmitter, Figure 1-1 illustrates the receiving coil as capturing the magnetic field of the power pick-up unit. A power pick-up unit typically contains a single receiving coil only. Moreover, a Mobile Device typically contains a single power receiver. The communications and control unit regulates the transferred power to the level that is appropriate for the subsystems (e.g., battery) connected to the output of the power receiver. These subsystems represent the main functionality of the Mobile Device.


Transmitters

As an example from the 2017 version 1.2.2 of the Qi specification (referenced above), the A2 reference Qi low-power transmitter has a coil of 20 turns (in two layers) in a flat coil, wound on a form with a 19mm inner diameter and a 40mm outer diameter, with a below-coil shield of soft iron at least 4mm larger in diameter which gives an inductance of 24±1 microhenries. This coil is placed in a series resonant circuit with a 200 nF capacitor to yield a resonant circuit with a natural resonance at ~140 kHz when coupled to the receiver coil. This series
resonant circuit An LC circuit, also called a resonant circuit, tank circuit, or tuned circuit, is an electric circuit consisting of an inductor An inductor, also called a coil, choke, or reactor, is a incremental passivity, passive two-terminal electronic ...
is then driven by an
H-bridge An H-bridge is an electronic circuit 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of individual electronic component An electronic component is any basic discrete device or physical entity in an ...

H-bridge
switching arrangement from the DC source; at full power, the voltage in the capacitor can reach 50 volts. Power control is automatic; the Qi specification requires that the actual voltage applied be controllable in steps at least as small as 50 millivolts. Rather than down-regulate the charging voltage in the device, Qi chargers meeting the A2 reference use a PID (proportional-integral-derivative) controller to modulate the delivered power according to the primary cell voltage. Other Qi charge transmitters start their connections at 140 kHz, but can change frequencies to find a frequency with a better match, as the mutual inductance between transmitter and receiver coils will vary according to the standoff distance between transmitter and receiver coils, and thus the natural resonance frequency will vary. Different Qi reference designs have different coil arrangements, including oval coil and multi-coil systems as well as more complex resonance networks with multiple inductors and capacitors. These designs allow frequency-agile operation at frequencies from 105 to 205 kHz and with maximum resonant circuit voltages as high as 200 volts.


Receivers

The Qi power receiver hardware reference design 1, also from version 1.2.2 of the Qi specification, starts with a rectangular coil of wire 44 mm x 30 mm outside size, with 14 turns of wire, and with an above-coil magnetic shield. This coil is wired into a parallel resonant circuit with a pair of capacitors (of 127 nanofarads in series and 1.6 nanofarads in parallel). The power output is taken across the 1.6 nanofarad capacitor. In order to provide a digital communications channel back to the power transmitter, a resonance modulator consisting of a pair of 22 nanofarad capacitors and a 10 kΩ resistor in a T configuration can be switched across the 1.6 nanofarad capacitor. Switching the T network across the 1.6 nanofarad capacitor causes a significant change in the resonant frequency of the coupled system that is detected by the power transmitter as a change in the delivered power. Power output to the portable device is via a full-wave
bridge A bridge is a structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules t ...

bridge
wired across the 1.6-nanofarad capacitor; the power is typically
filtered Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter m ...
with a 20-microfarad capacitor before delivery to the charge controller. Other Qi power receivers use alternate resonance modulators, including switching a resistor or pair of resistors across the receiver resonator capacitor, both before and after the bridge rectifier.


Features and specifications

left, The bottom side of an LG WCP-300 Qi charging pad The WPC published the Qi low-power specification in August 2009. The Qi specification can be downloaded freely after registration. Under the Qi specification, "low power" inductive transfers deliver power below 5 W using inductive coupling between two planar coils. These coils are typically 5 mm apart but can be up to 40 mm and possibly further apart. The Qi low-power specification has been renamed to the Qi Baseline Power Profile (BPP). Regulation of the output voltage is provided by a digital control loop where the power receiver communicates with the power transmitter and requests more or less power. Communication is unidirectional from the power receiver to the power transmitter via backscatter modulation. In backscatter modulation, the power-receiver coil is loaded, changing the current draw at the power transmitter. These current changes are monitored and demodulated into the information required for the two devices to work together. Opened Nokia DT-900 Qi charger In 2011, the Wireless Power Consortium began to extend the Qi specification to medium power. As of 2019, the Medium Power standard currently delivers 30 to 65 W, it is expected to eventually support up to 200 W (typically used for portable power tools, robotic vacuum cleaners, drones and e-bikes). In 2015, the WPC also demonstrated a high-power specification "Ki" that will deliver up to 1 kW, allowing the powering of kitchen appliances among other high-power utilities. In 2015, WPC introduced the Qi Extended Power Profile (EPP) specification which supports up to 15 W. EPP is also typically used to charge mobile devices like BPP. Phone companies that support EPP include
LG Electronics LG Electronics Inc. () is a South Korean Multinational corporation, multinational electronics company headquartered in Yeouido-dong, Seoul, South Korea. LG Electronics is a part of the LG Corporation, the fourth-largest ''chaebol'' in South K ...

LG Electronics
,
Sony , commonly known as Sony and stylized as SONY, is a Japanese multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from mult ...

Sony
,
Xiaomi Xiaomi Corporation (; ), registered in Asia as Xiaomi Inc., is a Chinese designer and manufacturer of consumer electronics Consumer electronics or home electronics are electronic Electronic may refer to: *Electronics Electronics ...

Xiaomi
, and
Sharp Corporation is a Japanese multinational corporation A multinational company (MNC) is a corporate A corporation is an organization—usually a group of people or a company A company, abbreviated as co., is a Legal personality, legal entity ...
. WPC introduced Proprietary Power Delivery Extension (PPDE) to allow phone OEMs to deliver higher than Baseline Power Profile's 5W or the Extended Power Profile's 15W. Currently only
Samsung The Samsung Group (or simply Samsung) ( ko, 삼성) is a South Korean Multinational corporation, multinational manufacturing Conglomerate (company), conglomerate headquartered in Samsung Town, Seoul, South Korea. It comprises numerous affil ...
has published their compliance test. Other phone companies that use proprietary standards for fast wireless charging include
Apple An apple is an edible fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this fie ...
,
Huawei Huawei Technologies Co., Ltd. ( ; ) is a Chinese multinational corporation, multinational technology company, technology corporation headquartered in Shenzhen, Guangdong, China. It designs, develops and sells telecommunications equipment, cons ...
and
Google Google LLC is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational stat ...

Google
.


Adoption

Nokia Nokia Corporation (natively Nokia Oyj, referred to as Nokia; stylized as NOKIA) is a Finnish multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational for ...

Nokia
first adopted Qi in its
Lumia 920 Nokia Lumia 920 is a smartphone A smartphone is a Mobile device, portable device that combines Mobile phone, mobile telephone and Mobile computing, computing functions into one unit. They are distinguished from feature phones by their strong ...

Lumia 920
, and
Samsung Mobile Samsung Mobile Division is one of five divisions within Samsung Electronics, belonging to the Samsung, Samsung Group, and consists of the Mobile Communications Division, Telecommunication Systems Division, Computer Division, MP3 Business Team, Mo ...
on the
Galaxy S3 The Samsung Galaxy S III (or Galaxy S3) is an Android Android may refer to: Science and technology * Android (robot), a humanoid robot or synthetic organism designed to imitate a human * Android (operating system), Google's mobile oper ...
(supported via a retrofittable official Samsung back cover accessory) in 2012,Wired
Qi Wireless Charging: What Is It And How Does It Work In Nokia's Lumia 920?
5 September 2012
the Google/LG
Nexus 4 The Nexus 4 (codenamed Mako) is an Android Android may refer to: Science and technology * Android (robot), a humanoid robot or synthetic organism designed to imitate a human * Android (operating system), Google's mobile operating system ** A ...

Nexus 4
followed later that year.
Toyota is a Japanese multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational state, a sovereign st ...

Toyota
began offering a Qi charging cradle as a factory option on its 2013 ,The Verge
Toyota's 2013 Avalon Limited becomes world's first car to adopt Qi wireless charging
19 December 2012
with
Ssangyong {{Infobox company , name = SsangYong Group , logo = SY sign.jpg , logo_caption = , image = , native_name = , native_name_lang = ko , hq_location_city = Seoul Seoul ( ...
the second car manufacturer to offer a Qi option, also in 2013.Torque News
Qi wireless charging system adopted by second automaker for use in cars
25 February 2013
In 2015, a survey found that 76% of people surveyed in the United States, United Kingdom, and China were aware of wireless charging (an increase from 36% the previous year), and 20% were using it — however only 16% of those using it were using it daily.IHS Markit
Consumer Awareness of Wireless Charging Doubles to 76 Percent in 2015, IHS Says
24 June 2015
Furniture retailer
IKEA#REDIRECT IKEA ''IKEA'' () is a Swedish multinational conglomerate that designs and sells , kitchen appliances and home accessories, among other useful goods and occasionally home services. Founded in Sweden Sweden (; sv, Sverige ), offic ...
introduced lamps and tables with integrated wireless chargers for sale in 2015, and the
Lexus NX The is a compact luxury crossover SUV A crossover, crossover SUV, or crossover utility vehicle (CUV) is a type of sport utility vehicle-like vehicle built with unibody, unibody frame construction. Crossovers are often based on a car platfo ...
gained an optional Qi charging pad in the center console. An estimated 120 million wirelessly charging phones were sold that year, notably the
Samsung Galaxy S6 The Samsung Galaxy S6 is a line of Android (operating system), Android-based smartphones manufactured, released and marketed by Samsung Electronics. Succeeding the Samsung Galaxy S5, the S6 was not released as a singular model, but instead in t ...

Samsung Galaxy S6
, which supported both Qi and the competing
Power Matters Alliance Power Matters Alliance (PMA) was a global, not-for-profit, industry organization whose mission was to advance a suite of standards and protocols for wireless power transfer for mobile electronic devices (specifically a type of inductive charging ...
standards.Wired
Wireless Charging Is Still a Mess, But It Won't Be Forever
12 November 2015
However, the existence of several competing wireless charging standards was still seen as a barrier to adoption. By early 2017, Qi had displaced other competing standards, with no new products featuring
Rezence (wireless charging standard) Official Rezence brandmark, the A4WP uses this mark of interoperability to show that various devices are compatible with Rezence systems. Rezence (pronounced reh-zense) is an interface standard developed by the Alliance for Wireless Power (A4WP) f ...
.E&T
Qi wireless charging standard emerges victorious; adoption rapidly increasing
17 February 2017
On September 12, 2017,
Apple Inc. Apple Inc. is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational state, ...
announced that their new smartphones, the
iPhone 8 The iPhone 8 and iPhone 8 Plus are smartphone A smartphone is a portable device A mobile device (or handheld computer) is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical ...

iPhone 8
,
iPhone 8 Plus The iPhone 8 and iPhone 8 Plus are smartphone A smartphone is a portable device A mobile device (or handheld computer) is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical ...

iPhone 8 Plus
, and the
iPhone X The iPhone X (Roman numeral Roman numerals are a that originated in and remained the usual way of writing numbers throughout Europe well into the . Numbers in this system are represented by combinations of letters from the . Modern style ...

iPhone X
, would support the Qi standard. Since then, every new iPhone version has supported the Qi wireless charging standard. Apple also announced plans to expand the standard with a new protocol called
AirPower Airpower or air power consists of the application of military aviation Military aviation comprises military aircraft A military aircraft is any fixed-wing A fixed-wing aircraft is a heavier-than-air flying machine, such as an airpl ...
which would have added the ability to charge multiple devices at once; however, this was canceled on March 29, 2019. As the Qi standard gains popularity, it is expected that ''Qi Hotspots'' will begin to arise in places such as coffee shops, airports, sports arenas, etc. The Coffee Bean and Tea Leaf, a major US coffee chain, will install inductive charging stations at selected major metropolitan cities, as well as
Virgin Atlantic Virgin Atlantic, a trading name A trade name, trading name, or business name is a pseudonym A pseudonym () (originally: ψευδώνυμος in Greek) or alias () is a fictitious name that a person or group assumes for a particular pur ...

Virgin Atlantic
, for United Kingdom's
London Heathrow Airport Heathrow Airport (), originally called ''London Airport'' until 1966 and now known as London Heathrow , is a major international airport An international airport is an airport An airport is an aerodrome An aerodrome (Commonwe ...

London Heathrow Airport
and New York City's
John F. Kennedy International Airport John F. Kennedy International Airport (colloquially referred to as JFK Airport) is an international airport in Queens, New York City, and one of the primary airports serving New York City. The airport is the busiest international air passeng ...
. Automobile manufacturers have been adding QI charging as standard or optional features since 2013.


Version history


See also

*
Near field communication Near-field communication (NFC) is a set of communication protocols A communication protocol is a system of rules that allows two or more entities of a communications system 400px, Communication system A communications system or communica ...
* WiPower *
Open DotsOpen Dots is a specification for conductive wireless charging, conductive wireless power technology for charging devices. It is overseen by the Open Dots Alliance, a 501(c) organization#501.28c.29.286.29, 501(c)(6) non-profit organization formed by ...
*
MagSafe MagSafe is a series of proprietary {{Short pages monitor