Imagine, for a moment, that you are a medical technician in a metropolitan emergency room. You move from room to room assisting the medical staff with portable diagnostic equipment. Tension is high and patients are non-stop – you don’t have the time to search for outlets to plug in your equipment.
You would prefer to drop it on a surface and have it charge automatically so you can move on to the next patient, injured people depend on a fast and efficient ER staff. Fortunately for you and the patients, wireless charging has become a technology of the present.
Evidence that wireless charging is gaining traction comes in the form of an industry standard specification. The Wireless Power Consortium’s (WPC) standard known as Qi (pronounced “chee”). This specification is separated into three key areas of the system – the power transmitter, the power receiver, and the communication protocol between the two devices. The main features of the standard are (see block diagram below):
Source: Wireless Power Consortium Website
- A method of contactless power transfer from a Base Station to a Portable Device, which is based on near field magnetic induction between coils.
- Transfer of around 5 W of power, using a secondary (or receiving) coil.
- Operation frequency in the range of 110 to 205 kHz.
- Support for two methods of placing the portable device on the surface of a base station: 1. A means of guiding the position of the Portable Device on the surface of a Base Station that provides power through a single or several fixed locations of that surface. 2. Free positioning which enables arbitrary placement of the Portable Device on the surface of a Base Station that can provide power through any location of that surface.
- Very low stand-by power achievable, depending on implementation.
- Design flexibility for the integration of the system into a Portable Device.
- A simple communication protocol enabling the Portable Device to take full control of the power transfer.
The power transfer process occurs in four phase
s:The Selection Phase
– the power transmitter monitors the charging interface to detect placement of a device to be charged. If none is detected the power transmitter will continuously ping the power receiver. If there is no device to be charged for a set amount of time the power transmitter will go into standby mode.The Ping Phase
– Similar to SONAR, the power transmitter issues a digital ping to detect a chargeable device. If a device is detected the power transmitter will maintain the power signal at the level of the ping and will go to the identification and configuration phase. If no device is detected, the power transmitter returns to the selection phase. The Identification and Configuration Phase
– The power transmitter negotiates with the power receiver to determine the amount of power needed to charge the device on the interface. If the device is removed from the interface the power transmitter returns to the selection phase. The Power Transfer Phase
– The power transmitter provides power to the power receiver adjusting current as needed based on feedback from the power receiver. Safety features are in place to shut down the power transfer and return to the selection phase should an anomaly occur in the power transfer process. This standard is already supported by over 90 companies in various fields of the electronics industry.Technology
Wireless power charging utilizes near-field magnetic induction to transfer power from a charging base station (pad) to a portable device. A transmitter coil (Tx) in the charging pad sends power over varying distances to a receiver coil (Rx) embedded in a portable device like a cell phone.
The Transmitter/Primary coil inside the charging pad creates a magnetic field when powered, similar to a conventional transformer, inducing current to flow through the secondary coil that's attached to the portable device. (The charging pad has a power conversion circuitry that converts electrical power to magnetic field. At the receiver end; the power pickup unit converts the magnetic field back to electrical power to charge the device’s battery). The transmitter and receiver communicate with each other to control the charging process.
The Vishay Dale Electronics IWAS Series Qi wireless charging receiving coil/shield offers the first commercially available wireless receiver coil for the WPC compliant devices. The IWAS Series provides 70% or greater efficiency with high permeability shielding for the receiving coil, and blocks charging flux from damaging sensitive components or batteries. The IWAS coil/shield performance is not adversely affected by permanent locating magnets.