5

Device description

5.1

Wireless power interface

Wireless charging system diagram is shown below. The key blocks are Inverter (Power conversion unit),

Communications and Control unit.

The Tx is responsible for controlling the transmitting coil and transferring the correct amount of power requested

by the Rx.

The Rx modulates the power signal using resistive and capacitive load to communicate to the Tx requested power

level.

Transferring the correct amount of power ensures the highest level of end to-end efficiency due to reduced energy

losses. It also helps maintaining a lower operational temperature.

The Tx can adapt to the amount of energy transferred by the coil by adjusting the frequency, duty cycle of the

PWM voltage on the transmitting coil.

Figure 3. Wireless charging system

5.2

Inverter

The power transmitter design uses a Full bridge inverter to drive the primary coil and series capacitance. The

power transmitted to the coil is regulated by varying switching frequency and/or duty cycle of the bridge.

A higher operating frequency (for example 200kHz) leads to lower transmitted power, while a lower frequency (for

example 110kHz) leads to higher transmitted power.

The LC resonant circuit optimization to be done based on power transfer requirements.

Full bridge inverter circuit is shown below.

STWBC86

Device description

DS14079 - Rev 1

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