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Wireless Charger Basics: Types, Standards, and Manufacturers

wireless charging qi standard inductive charging resonance charging power

Our lives are increasingly reliant on wireless electronic devices powered by batteries, making efficient battery charging crucial.

In the early days, wireless charging was less appealing than wired options due to longer charging times and lower current output. However, the Wireless Power Consortium (WPC) introduced the Qi power standard in 2008, using inductive charging. Initially, these chargers delivered limited current (around 5 Watts). Recent advancements have allowed Qi devices to deliver up to 120 Watts, with currents reaching approximately 1 Ampere.

wireless charger Figure depicts Qi compliant wireless charging pad model WCP 300 from LG.

Various standards are emerging to support wireless charging demands from consumers and the mobile market. Notable examples include the Power Matter Alliance (PMA) and Alliance for Wireless Power (A4WP). Devices like the BCM59359 from Broadcom can wirelessly charge devices compliant with any of these standards.

Wireless Charger Types

There are two primary types of wireless chargers:

  • Inductive Charging: This method utilizes two coils: a primary coil connected to the AC mains and a secondary coil. Magnetic flux is generated in the secondary coil through induction, producing the current needed to charge the device.
  • Resonance Charging: Based on the A4WP standard, this type allows multiple devices to be charged wirelessly within the range of a wide resonant field. A4WP-compliant chargers operate at a standard international frequency of 6.78KHz, with 2.4GHz used for control and management.

The key difference lies in the coupling factor: inductive charging has a higher coupling factor than resonance charging.

Wireless Charger Manufacturers

The wireless charger market is booming, driven by the proliferation of affordable electronic devices. Many companies manufacture devices compliant with various standards, producing components like single-coil power transmitters, power application controllers, slip rings, wireless connectors, power receivers, and charging PMUs.

Here is a list of some wireless charger manufacturers:

  • Freescale
  • NXP
  • Active-Semi
  • PowerbyProxi
  • TI
  • STMicroelectronics
  • Broadcom

Qi Wireless Charging Basics

For an understanding of Qi wireless charging and how it functions, refer to the Qi Wireless charging documentation.