Charging batteries without wires in a compact and efficient manner

April 07, 2014 //By Jean-Pierre Joosting
Batteries provide power to many different applications across a wide range of industries. In many of these applications, a charging connector is difficult or impossible to use.

For example, some products require sealed enclosures to protect sensitive electronics from harsh environments and to allow for convenient cleaning or sterilization. Other products may simply be too small to include a connector, and in products where the battery-powered application includes movement or rotation, then forget about charging with wires. Wireless charging adds value, reliability and robustness in these and other applications.

Wireless power system overview

As shown in Figure 1, a wireless power system is composed of two parts separated by a gap: transmit circuitry, including a transmit coil, and receive circuitry, including a receive coil. The transmit circuitry generates a high frequency alternating magnetic field around the transmit coil. This magnetic field is coupled to the receive coil and converted to electrical energy, which can be used to charge a battery or power other circuitry.

When designing a wireless power charging system, a key parameter is the amount of charging power that actually adds energy to the battery. This received power depends on many factors, including the amount of power being transmitted, the distance and alignment between the transmit coil and the receive coil, also known as the coupling between the coils, and finally, the tolerance of the transmit and receive components.

Figure 1.

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