Shown here is the basic illustration of the hardware involved in the Qi wireless power system. The wireless power transmitter is typically a “charging pad” but can also be built into furniture like tables or desks. All the user has to do is place their phone (or other wirelessly powered device) on the right spot on the table or pad, and the device’s battery will begin charging with no mechanical connections required. The transmit side takes in DC power from a wall adapter. This DC level may vary depending on the type of transmit controller used. TI solutions may operate from +5, +12, or +19 VDC depending on the specific TX chip selected. The DC input to the TX controller is then converted into a quasi-sinusoidal AC signal across the transmit coil. A resonant converter is used in most implementations. The frequency is in the 100 to 200 KHz range, with the resonant peak being at the low end of the range. The wireless receiver is built into the handheld device (which could be a mobile phone, camera, or other portable equipment). The receiver coil picks up the AC excitation from the transmitter and then this voltage is rectified and regulated to provide up to 5 W of DC power at the output. The receiver also provides feedback to the transmitter via digital communication that is carried across the same RF coupling as the power in the forward direction. “From a distance” this circuit really looks just like any other transformer-coupled supply…except that in this case, the primary and secondary coils are in separate housings instead of being wound on the same magnetic core. Power is inductively coupled from the TX coil to the RX coil. To ensure reasonable efficiency, and to minimize noise generated in the nearby environment, a specific type of design is required for the TX and RX coils, and good alignment along with proper shielding is required.