New Industry Products

# Complete AirFuel Alliance Compatible Wireless Power Demo Kit

June 02, 2018 by Paul Shepard

Efficient Power Conversion Corporation (EPC) today announces the availability of a complete class 4 wireless power kit, the EPC9129. The system can transmit up to 33W while operating at 6.78MHz (the lowest ISM band). The kit comes complete with two receivers, each with a regulated output − one capable of 5W capable and a second capable of delivering 27W at 19V.

The purpose of this demonstration kit is to simplify the evaluation process of using eGaN FETs for highly efficient wireless power transfer. The EPC9129 utilizes the high frequency switching capability of EPC gallium-nitride transistors to facilitate wireless power systems with full power efficiency between 80% and 90% under various operating conditions.

The popularity of highly resonant wireless power transfer is increasing rapidly, particularly for applications targeting large power transmitting surface areas, with the capability to place receiving devices anywhere on the surface, and the ability to simultaneously power (or charge) multiple devices placed on the surface.

The end applications are varied and evolving quickly from cell phone charging to powering handheld tablets and laptop computers.  Delivering up to 33 W supports all of these applications.

The EPC9129 wireless power system consists of four boards:

• Source Board (Transmitter or Power Amplifier) EPC9512 featuring the EPC8010, EPC2038 and EPC2019
• Class 4 Air Fuel compliant Source Coil (Transmit Coil)
• Category 5 AirFuel compatible Receive Device EPC9514 featuring the EPC2016C
• Category 3 AirFuel compatible Receive Device EPC9513 featuring the EPC2019

#### Source (Amplifier) Board

The source board is a highly efficient Zero Voltage Switching (ZVS), Class-D amplifier configured in an optional half-bridge topology (for single-ended con­figuration) or default full-bridge topology (for differential configuration), and includes the gate driver(s), oscillator, and feedback controller for the pre-regulator. This allows for compliance testing operating to the AirFuel class 4 standard over a wide load range.

The amplifier board is available separately as EPC9512 for evaluation in existing customer systems.

#### Device (Receiving) Boards

The Category 5 EPC9514 (19 V, 27 W) and Category 3 EPC9513 (5 V, 5 W) device or receiving boards included in the wireless power demonstration kits are also available separately for those that have their own source boards or who want to work with multiple receiving devices simultaneously. The efficiency of these first-generation systems is about 87% from input to the transmitter to the output of the receiver (end-to-end), and with future improvements in architecture and GaN IC technology this number can reach into the 95% range.

As with the demonstration kits, these boards operate to the Airfuel standard, excluding Bluetooth Low Energy (BLE) communications.

With the wide range of efficient receivers that can be used to power anything from lamps to laptops to tablets, while remaining compatible with cell phone charging, the system designer now has all the tools needed to create an entire wireless power, large area, efficient system.

#### Price and Availability

EPC9129 wireless power transfer demonstration systems are priced at $907.20 each. The EPC9512 amplifier board can also be purchased separately and is priced at$390.00 each

The EPC9513 and EPC9514 receive boards can also be purchased separately and are priced at \$168.75 each.  All products are available for immediate delivery from Digi-Key.

The amplifier board (EPC9512) features the enhancement-mode, 100V-rated EPC8010 eGaN FET as the main power stage in a dual half-bridge configuration; the 100V-rated EPC2038 eGaN FET used as the synchronous bootstrap FET, and the 200V-rated EPC2019 eGaN FET used in the SEPIC pre-regulator. The amplifier can be set to operate in either differential mode or single-ended mode and includes the gate driver(s), oscillator, and feedback controller for the pre-regulator that ensures operation for wireless power control based on the AirFuel standard.

Diagram of EPC9512 ZVS class-D amplifier circuit (click on image to enlarge)

The EPC9512 can operate in either single-ended or differential mode by changing a jumper setting. This allows for high efficiency operation with load impedance ranges suitable for single ended operation. The circuits used to adjust the timing for the ZVS class-D amplifiers have been separated to further ensure highest possible efficiency setting. Each half bridge also includes separate ZVS tank circuits.

Block diagram of the EPC9512 wireless power amplifier (click on image to enlarge)

The amplifier is equipped with a pre-regulator controller that adjusts the voltage supplied to the ZVS class-D amplifier based on the limits of 3 parameters: coil current, DC power delivered to the ZVS class-D amplifier, and maximum operating voltage of the ZVS class-D amplifier.

The coil current has the lowest priority followed by the power delivered and amplifier supply voltage having the highest priority. Changes in the device load power demand, physical placement of the device on the source coil and other factors, such as metal objects in proximity to the source coil, contribute to variations in coil current, DC power, and amplifier voltage requirements. Under any of these conditions, the controller will ensure the correct operating conditions for the ZVS class-D amplifier based on the AirFuel standard.

The pre-regulator can be bypassed to allow testing with custom control hardware. The board further allows easy access to critical measurement nodes for accurate power measurement instrumentation hookup.

The source and device coils are AirFuel compliant and have been pretuned to operate at 6.78 MHz with the EPC9512 amplifier. The source coil is AirFuel class 4 compliant and the device coils are AirFuel category 3 and category 5 compliant. The EPC9513 (Category 3) device board includes a high frequency Schottky diode based full-bridge rectifier, DC smoothing capacitor and 5 V regulator. The regulator is based on a SEPIC converter that features a 200 V EPC2019 eGaN FET. The power circuit is attached to the backside of the coil which is provided with a ferrite shield that prevents the circuit from shunting the coil’s magnetic field.

Schematic diagram of the EPC9513 and EPC9514 demo board (click on image to enlarge)

The EPC9514 (Category 5) device board includes a high frequency Schottky diode based full-bridge rectifier, DC smoothing capacitor and 19 V regulator. The regulator is based on a SEPIC converter that features a 100 V EPC2016C eGaN FET. The power circuit is attached to the side of the coil.