Wireless Charging - The emerging trend

Many of us use a wall mount charger for charging out multimedia devices like smartphones, tablets, music devices, etc. These devices have a socket into which the external charger goes in. It is always recommended that you use a suggested charger for a specific device. What if you don't have to use this wired charger and charge your mobile hassle free? Yes, this is what wireless charging is. Just place your mobile on a charging pad and your mobile gets charged, as simple as that.

Wireless charging is based on the principle of magnetic induction. Magnetic induction meant there will be two coils in which the first coil (transmitter) has a current flowing through it which causes magnetic flux. when the second coil (receiver) is placed near to first coil the magnetic flux induces current in the second coil. So, a charging pad on which you place the mobile will have a coil in which flux will be developed. When you place your mobile right next to the charging pad, which has a second coil , it induces current and hence battery charges. Basically, it is the electromagnetic field that plays a role here.

An alternative to magnetic induction is resonant charging. In this the receiver need not be next to the transmitter. Both of them work on the principle of resonance. In this way of charging power is transmitted wireless at a 6.78 MHz rate. In this case, the resonance helps charging.

What are the various wireless charging standards?

• A4WP (Alliance for wireless power)
• PMA (Power Matter Allaince)
• WPC (Wireless power consortium)

WPC developed Qi standard which is the most popular now and is in use. Qi is basically the magnetic induction type of charging. Regulatory approvals are in place for this standard.

A4WP developed resonant type charging. Regulatory approvals not in place.

What are the challenges from the designer point of view?

Let us take a smartphone designer, who wants to implement wireless charging in his device. The challenge for him is to select a chipset which is used as receiver. The chip has to support the desired standard. Also, the charging control circuitry to be implemented to connect to unit to be charged (battery). Chip sets are also available in the market which supports various charging standards. Coupling factor is of primary importance. A higher coupling factor leads to faster charging rate.

What are the various vendors for wireless charging chips?

• IDT
• Broadcom
• NXP
• Texas Instruments
• Freescale
• STMicroelectronics

What are the various domains wireless charging is expected to get exposed to?

• Smartphone charging where the charge pads can be mounted outdoors at public places like bus stops, cafeterias.
• Electric vehicles charging (Battery)

What are the differences between Inductive charging and resonant charging?

• For inductive charging, the receiver must be in the close proximity of transmitter (receiver and transmitter separated by centimeter distance) where as for resonant charging this is not the case.
• Coupling factor is high in inductive charging
• Size of the coils is more in inductive charging than resonant charging
• Cost is also high for inductive charging than resonant charging
• Efficiency is high in inductive charging
• Heat is more in inductive charging