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51-570: The Qi standard is developed by the Wireless Power Consortium . As a universal, open standard Qi-enabled devices are able to connect to Qi chargers from any manufacturer. Qi was first released in 2008; by 2017, it was incorporated into more than 200 smartphones, tablets and other devices. As of December 2023, there are 351 manufacturers working with the standard including Apple , Asus , Google , Huawei , LG Electronics , Samsung , Xiaomi , and Sony . In January 2023,

102-423: A resonant circuit , tank circuit , or tuned circuit , is an electric circuit consisting of an inductor , represented by the letter L, and a capacitor , represented by the letter C, connected together. The circuit can act as an electrical resonator , an electrical analogue of a tuning fork , storing energy oscillating at the circuit's resonant frequency . LC circuits are used either for generating signals at

153-692: A Qi charging cradle as a factory option on its 2013 Avalon Limited , with Ssangyong the second car manufacturer to offer a Qi option, also in 2013. As the Qi standard gained popularity, Qi Hotspots began to arise in places such as coffee shops, airports, sports arenas, etc. In 2012, The Coffee Bean and Tea Leaf , a major US coffee chain, announced plans to install inductive charging stations at selected major metropolitan cities, as did Virgin Atlantic , for United Kingdom's London Heathrow Airport , and New York City's John F. Kennedy International Airport . In 2015,

204-423: 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 –

255-455: A current to begin to recharge the capacitor with a voltage of opposite polarity to its original charge. Due to Faraday's law , the EMF which drives the current is caused by a decrease in the magnetic field, thus the energy required to charge the capacitor is extracted from the magnetic field. When the magnetic field is completely dissipated the current will stop and the charge will again be stored in

306-545: A particular frequency, or picking out a signal at a particular frequency from a more complex signal; this function is called a bandpass filter . They are key components in many electronic devices, particularly radio equipment, used in circuits such as oscillators , filters , tuners and frequency mixers . An LC circuit is an idealized model since it assumes there is no dissipation of energy due to resistance . Any practical implementation of an LC circuit will always include loss resulting from small but non-zero resistance within

357-577: A positive number). At one particular frequency, these two reactances are equal and the voltages across them are equal and opposite in sign; that frequency is called the resonant frequency f 0   for the given circuit. Hence, at resonance, Solving for ω , we have which is defined as the resonant angular frequency of the circuit. Converting angular frequency (in radians per second) into frequency (in Hertz ), one has and at ω 0 {\displaystyle \omega _{0}} . In

408-431: 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

459-481: 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 ; the Mobile Device contains a power receiver holding a receiving coil. The magnetic field induces an alternating current in the receiving coil by Faraday's law of induction . Close spacing of

510-399: A series configuration, X C and X L cancel each other out. In real, rather than idealised, components, the current is opposed, mostly by the resistance of the coil windings. Thus, the current supplied to a series resonant circuit is maximal at resonance. In the series configuration, resonance occurs when the complex electrical impedance of the circuit approaches zero. First consider

561-601: A survey found that 76% of people surveyed in the United States and China were aware of wireless charging (an increase from 36% the previous year), and 20% were using it – however, only 16% of those were using it daily. Furniture retailer IKEA introduced lamps and tables with integrated wireless chargers for sale in 2015, and the Lexus NX gained an optional Qi charging pad in the center console. An estimated 120 million wirelessly charging phones were sold that year, notably

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612-488: 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

663-510: Is where L is the inductance in henries , and C is the capacitance in farads . The angular frequency ω 0 has units of radians per second. The equivalent frequency in units of hertz is The resonance effect of the LC circuit has many important applications in signal processing and communications systems. LC circuits behave as electronic resonators , which are a key component in many applications: By Kirchhoff's voltage law ,

714-462: Is placed in a series resonant circuit. This series resonant circuit is then driven by 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

765-400: Is the simplest type of inductor-capacitor network (or LC network ). It is also referred to as a second order LC circuit to distinguish it from more complicated (higher order) LC networks with more inductors and capacitors. Such LC networks with more than two reactances may have more than one resonant frequency . The order of the network is the order of the rational function describing

816-713: The Galaxy Note 5 and S6 edge plus , August 2015) requires charging plate to be connected to Qualcomm Quick Charge 2.0-enabled 15 W USB charger (9-volt, 1.67-ampere support). Wireless Power Consortium Too Many Requests If you report this error to the Wikimedia System Administrators, please include the details below. Request from 172.68.168.236 via cp1112 cp1112, Varnish XID 942498668 Upstream caches: cp1112 int Error: 429, Too Many Requests at Thu, 28 Nov 2024 08:30:17 GMT Resonant circuit An LC circuit , also called

867-495: The Samsung Galaxy S6 , which supported both Qi and the competing Power Matters Alliance standards. 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 such as Rezence . On September 12, 2017, Apple announced that their new smartphones, the iPhone 8 , iPhone 8 Plus , and the iPhone X , would support

918-462: The current through it. If an inductor is connected across a charged capacitor, the voltage across the capacitor will drive a current through the inductor, building up a magnetic field around it. The voltage across the capacitor falls to zero as the charge is used up by the current flow. At this point, the energy stored in the coil's magnetic field induces a voltage across the coil, because inductors oppose changes in current. This induced voltage causes

969-536: The impedance of the series LC circuit. The total impedance is given by the sum of the inductive and capacitive impedances: Writing the inductive impedance as Z L = jωL   and capacitive impedance as Z C = ⁠ 1 / j ω C   ⁠   and substituting gives Writing this expression under a common denominator gives Finally, defining the natural angular frequency as the impedance becomes where ω 0 L   {\displaystyle \,\omega _{0}L\ \,} gives

1020-652: The Extended Power Profile's 15 W. Currently, only Samsung has published their compliance test. Other phone companies that use proprietary standards for fast wireless charging include Apple, Huawei and Google. Nokia first adopted Qi in its Lumia 920 , and Samsung Mobile on the Galaxy S3 (supported via a retrofittable official Samsung back cover accessory) in 2012, the Google/LG Nexus 4 followed later that year. Toyota began offering

1071-486: 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

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1122-456: 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

1173-428: The Qi specification, starts with a rectangular coil of wire 44 mm × 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

1224-432: 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 which would have added the ability to charge multiple devices at once; however, this was canceled on March 29, 2019. By the initial launch of the iOS 17 in 2023, Apple launched the iPhone 15 models and iPhone 15 Pro models to support

1275-691: The WPC also demonstrated a high-power specification, called "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 , Sony , Xiaomi , and Sharp . WPC introduced Proprietary Power Delivery Extension (PPDE) to allow phone OEMs to deliver higher than Baseline Power Profile's 5 W or

1326-411: The announcement of the iPhone 16 models and iPhone 16 Pro models, Apple launched the new fast 25W MagSafe charger to feature the woven braided cable design, available in 1m and 2m length options and maintaining the compatibility with the fast 15W Qi2-certified wireless charging. Extended Power Profile (EPP): 15 W Labeled by Samsung as "Fast Wireless Charging" (initially 10 W, introduced on

1377-527: The capacitance and inductance values. In most applications the tuned circuit is part of a larger circuit which applies alternating current to it, driving continuous oscillations. If the frequency of the applied current is the circuit's natural resonant frequency ( natural frequency f 0 {\displaystyle f_{0}\,} below), resonance will occur, and a small driving current can excite large amplitude oscillating voltages and currents. In typical tuned circuits in electronic equipment

1428-407: The capacitor, with the opposite polarity as before. Then the cycle will begin again, with the current flowing in the opposite direction through the inductor. The charge flows back and forth between the plates of the capacitor, through the inductor. The energy oscillates back and forth between the capacitor and the inductor until (if not replenished from an external circuit) internal resistance makes

1479-541: The circuit is equal to the current through both the capacitor and the inductor. Inductive reactance   X L = ω L   {\displaystyle \ X_{\mathsf {L}}=\omega L\ } increases as frequency increases, while capacitive reactance   X C = 1   ω C     {\displaystyle \ X_{\mathsf {C}}={\frac {1}{\ \omega C\ }}\ } decreases with increase in frequency (defined here as

1530-431: The components and connecting wires. The purpose of an LC circuit is usually to oscillate with minimal damping , so the resistance is made as low as possible. While no practical circuit is without losses, it is nonetheless instructive to study this ideal form of the circuit to gain understanding and physical intuition. For a circuit model incorporating resistance, see RLC circuit . The two-element LC circuit described above

1581-455: The consortium announced Qi2, which will update the existing standard and include a magnetic connection based on Apple's MagSafe technology. On April 19, 2023, Wireless Power Consortium released the Qi2 standard. Devices that operate using the Qi standard rely on electromagnetic induction between planar coils . A Qi system consists of two types of devices – the Base Station, which is connected to

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1632-452: 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

1683-439: The electric current I is a physical quantity, it must be real-valued. As a result, it can be shown that the constants A and B must be complex conjugates : Now let Therefore, Next, we can use Euler's formula to obtain a real sinusoid with amplitude I 0 , angular frequency ω 0 = ⁠ 1 / √ LC ⁠ , and phase angle ϕ {\displaystyle \phi } . Thus,

1734-406: The fast 15W Qi2-certified wireless charging. Prior to the launch of the iOS 17.2 , Apple added the fast 15W Qi2-certified wireless charging support for the iPhone 13 models, iPhone 13 Pro models, iPhone 14 models and iPhone 14 Pro models, but all the iPhone 12 models and iPhone 12 Pro models have limited support to the 5W Qi-certified wireless charging. On September 9, 2024, alongside

1785-419: The main line (in principle, zero current). However, there is a large current circulating between the capacitor and inductor. In principle, this circulating current is infinite, but in reality is limited by resistance in the circuit, particularly resistance in the inductor windings. Since total current is minimal, in this state the total impedance is maximal. The resonant frequency is given by Any branch current

1836-481: The network in the complex frequency variable s . Generally, the order is equal to the number of L and C elements in the circuit and in any event cannot exceed this number. An LC circuit, oscillating at its natural resonant frequency , can store electrical energy . See the animation. A capacitor stores energy in the electric field ( E ) between its plates, depending on the voltage across it, and an inductor stores energy in its magnetic field ( B ), depending on

1887-411: The oscillations are very fast, from thousands to billions of times per second. Resonance occurs when an LC circuit is driven from an external source at an angular frequency ω 0 at which the inductive and capacitive reactances are equal in magnitude. The frequency at which this equality holds for the particular circuit is called the resonant frequency. The resonant frequency of the LC circuit

1938-410: The oscillations die out. The tuned circuit's action, known mathematically as a harmonic oscillator , is similar to a pendulum swinging back and forth, or water sloshing back and forth in a tank; for this reason the circuit is also called a tank circuit . The natural frequency (that is, the frequency at which it will oscillate when isolated from any other system, as described above) is determined by

1989-518: The output of the power receiver. These subsystems represent the main functionality of the Mobile Device. 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 19 mm inner diameter and a 40 mm outer diameter, with a below-coil shield of soft iron at least 4 mm larger in diameter which gives an inductance of 24 ± 1 microhenries. This coil

2040-416: The portable device is via a full-wave bridge wired across the 1.6-nanofarad capacitor; the power is typically filtered 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. The WPC published

2091-422: 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

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2142-604: The power transmitter. These current changes are monitored and demodulated into the information required for the two devices to work together. 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,

2193-424: The reactance of the inductor at resonance. The numerator implies that in the limit as ω → ± ω 0   , the total impedance Z  will be zero and otherwise non-zero. Therefore the series LC circuit, when connected in series with a load, will act as a band-pass filter having zero impedance at the resonant frequency of the LC circuit. When the inductor (L) and capacitor (C) are connected in parallel as shown here,

2244-423: The resonant angular frequency , is defined as Using this can simplify the differential equation: The associated Laplace transform is thus where j is the imaginary unit . Thus, the complete solution to the differential equation is and can be solved for A and B by considering the initial conditions. Since the exponential is complex , the solution represents a sinusoidal alternating current . Since

2295-399: The resulting solution becomes The initial conditions that would satisfy this result are In the series configuration of the LC circuit, the inductor (L) and capacitor (C) are connected in series, as shown here. The total voltage V across the open terminals is simply the sum of the voltage across the inductor and the voltage across the capacitor. The current I into the positive terminal of

2346-419: 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

2397-535: 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. The Qi power receiver hardware reference design 1, also from version 1.2.2 of

2448-406: 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

2499-627: The two coils ensures 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 –

2550-405: The voltage V C across the capacitor plus the voltage V L across the inductor must equal zero: Likewise, by Kirchhoff's current law , the current through the capacitor equals the current through the inductor: From the constitutive relations for the circuit elements, we also know that Rearranging and substituting gives the second order differential equation The parameter ω 0 ,

2601-446: The voltage V across the open terminals is equal to both the voltage across the inductor and the voltage across the capacitor. The total current I flowing into the positive terminal of the circuit is equal to the sum of the current flowing through the inductor and the current flowing through the capacitor: When X L equals X C , the two branch currents are equal and opposite. They cancel each other out to give minimal current in

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