Qi is a proprietary standard of the Wireless Power Consortium (WPC) for wireless energy transmission using electromagnetic induction over short distances. According to WPC, the Qi standard, which was founded in 2008, is supported by over 1000 different devices and counts over 200 companies among its members. The first supplier of smartphones was the South Korean manufacturer Samsung, whose Samsung Galaxy S III, released in 2012, could be retrofitted with Qi. Inductive charging became more widespread due to its fixed integration into the Nokia Lumia 2012 and 820, which were introduced in autumn 920. With the iPhone 2017 and iPhone X introduced in September 8, Apple smartphones also support Qi for the first time. Currently, there are also Qi fast chargers on the market with a power of 7 to 15 watts, which brings the charging time closer to that of USB chargers.
Qi uses a resonant inductive coupling between the transmitter and receiver. The transmitter and receiver exchange data to ensure optimal energy transmission. The transmitter modulates the transmission field. The receiver uses RFID-like technology to transmit data to the sender. Due to the typically high magnetic coupling of the coils, high power can be transmitted without exceeding EMC limits.
Pros of Qi
- All you have to do is hang up the device
- Devices and chargers can be from different manufacturers
- A single charger can be used for multiple devices
- Due to the fact that the bushing is no longer necessary, both electrically and mechanically:
- no wear and tear of plug contacts due to plugging and unplugging,
- better protection against ESD discharges,
- no mechanical weak points due to a bushing recess,
- No ingress of dust or water, so that it can also be used in harsh environments or with a higher IP rating,
in the coordination between PCB layout and package design, there is no need to match the positioning of a socket.
Cons of Qi
- During power transfer, the device must remain in physical contact with the charger; so it’s not so easy to make phone calls with a mobile phone anymore.
- Due to the loose inductive coupling, the efficiency of the charging process deteriorates compared to conventional charging by cable;
- Qi chargers are usually more expensive than traditional chargers.
- Interference with longwave broadcasting
- Increased heat generation due to eddy current losses compared to wired charging, which either causes components such as the accumulator to age faster or the charging power has to be reduced.