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Home » Applications & Technologies » Wireless Charging Technology Electronics
Applications & Technologies
Wireless Charging Overview

Qi (pronounced “Chee”) is the global wireless charging standard developed and licensed by the largest technology alliance in the wireless charging industry, the Wireless Power Consortium (WPC). An open platform with the support of nearly 150 WPC member companies, including major mobile phone manufacturers, wireless service providers, and semiconductor companies, and with well over 300 Qi-certified products introduced into the market since the specification was first introduced in 2009, Qi is helping to bring wireless charging of mobile devices into the mainstream. Products that carry the Qi logo on their packaging are interoperable, allowing consumers the freedom to charge any Qi-compliant device, given any Qi charger.

The Qi system consists of a flat charging pad, and a mobile device equipped with a compatible receiver. When the mobile is placed on top of the charging pad, the device is charged via electromagnetic induction. Essentially, an alternating current passed through a coil in the charging pad generates a magnetic field that induces a voltage in a coil in the receiver, which can then be used to power the mobile directly or charge the battery.

Qi provides for electrical power transfer up to 4 cm (1.6 inches), with typical efficiency around 70 percent, with 80 to 85 percent efficiency possible with careful design, better shielding, and newer techniques such as the use of ultra thin coils. The low-power specification that exists today delivers up to 5 watts to receivers, enough for smart phones and small mobile gadgets.

Wireless Charging Semiconductors
Wireless Charging SemiconductorsTI Qi-Compliant Wireless Power Transmitter

Since the introduction of the Wireless Power Consortium’s Qi standard in 2009, a number of integrated circuit solutions for Qi-compliant wireless charging have become available. Today’s Qi semiconductor offerings integrate all of the necessary intelligence, control, power management, and communication functionalities into tiny micro-packages, enabling end equipment designers to achieve high performance and efficiency goals, while meeting competitive cost, small-size, and fast time-to-market targets.

The Qi wireless power system consists of a charging pad housing a power transmitter, and a mobile device with a power receiver. When the mobile device rests on the charging pad, the receiver communicates to the transmitter, requesting the appropriate amount of power desired. The transmitter transfers power to the receiver via coupled inductors, with the primary coil in the transmitter, and the secondary coil in the receiver. The receiver sends feedback to the transmitter requesting more or less power, and the transmitter monitors and acts on this information as needed in the closed digital control loop. The charging pad powers down for most of the time to save energy, waking occasionally to check for the presence of a receiver. After a receiver is authenticated, the charging pad stays on.

» View Wireless Charging Semiconductors

Wireless Charging Passives
Wireless Charging
Vishay / Dale IWAS Series Wireless Charging Receiving Coil/Shield

Fundamentally important to achieving a Qi-compliant wireless charging system, is proper implementation of the magnetics. To help achieve this end, the Qi standard outlines the physical requirements for the transmitter and receiver coils, as well as their alignment and shielding. The standard also provides information on tuning the coils to resonance.

Transmitter (Primary) Coil and Matching Capacitor

The Qi specification lays out the different types of transmitter design implementations that are allowed. For each transmitter design, there is a specification section that strictly describes the respective coil, including shape, dimensions, materials, number of turns, and number of layers. Given the fixed parameters, certain catalog coils have been tested and approved for compatibility with particular power transmitter control ICs, simplifying the charging pad design process.

» View Storage Devices for Wireless Charging

Development Tools
Development tool example
Wireless Charging Development Tool from IDT

The most efficient way to develop end applications for Qi wireless charging is to start with available evaluation kits (EVK) or evaluation modules (EVM). These tools allow designers to easily and quickly demonstrate the features and performance of prospective devices, speeding the development effort. Some tools may even have received Qi certification by independent testing facilities, and therefore can be used as Qi-compliant reference designs.

Mouser stocks both Qi wireless power transmitter and Qi wireless power receiver evaluation modules. These are complete transmitter-side and receiver-side solutions, including all the necessary components, such as the coils to allow immediate evaluation. The receiver evaluation modules do need to be placed on a Qi-compliant wireless charging pad for testing, and likewise, the transmitter evaluation modules need to be paired with a Qi-compliant receiving device.

» View Wireless Charging Development Tools & Kits

Learn more about TI Qi-Compliant Transmitters & Receivers
TI Qi-Compliant
Transmitters & Receivers

  • Intelligent control of the power transfer
  • Conforms to the Wireless Power Consortium
  • Operating modes status indicators
Learn more about TI Qi-Compliant Transmitters & Receivers
Learn more about TDK Wireless Charging Coils
TDK Wireless
Charging Coils

  • Industry-leading thickness of 0.57mm
  • Ultra thin & light-weight
  • 0.5 to 0.6A output current
Learn more about TDK Wireless Charging Coils
Learn more about Vishay / Dale IWAS Qi Wireless Coil/Shields
Vishay / Dale IWAS Qi
Wireless Coil/Shields

  • High permeability shielding for coils
  • Blocks charging flux from sensitive components
  • Not affected by permanent locating magnets
Learn more about Vishay / Dale IWAS Qi Wireless Coil/Shields
Learn more about On Semi Dual 20V N-Channel MOSFETs
On Semi Dual 20V
N-Channel MOSFETs

  • Full-bridge rectifier block
  • Up to 3.2A operation
  • Low RDS(on) MOSFET to minimize conduction loss
Learn more about On Semi Dual 20V N-Channel MOSFETs
Learn more about IDT IDTP9030 Transmitter ICs for TX-A1
IDT IDTP9030 Transmitter
ICs for TX-A1

  • Single-Chip 5W solution
  • 19 ± 1V operating input voltage
  • Integrated half-bridge inverter
Learn more about IDT IDTP9030 Transmitter ICs for TX-A1
Learn more about Wurth Electronics Charging Coils
Wurth Electronics
Charging Coils

  • Wirelessly delivers power up to 5W
  • Operating temperature: -20°C to 105°C
  • Qi-standard compliant
Learn more about Wurth Electronics Charging Coils