EPC9113(#1): 16W, Class-D, Rezence (A4WP) Compatible

The EPC9113 wireless power demonstration system is a high efficiency, Rezence (A4WP) compatible, Zero Voltage Switching (ZVS), Voltage Mode class-D wireless power transfer demonstration kit capable of delivering up to 16 W into a DC load while operating at 6.78 MHz (Lowest ISM band). The purpose of this demonstration system is to simplify the evaluation process of wireless power technology using eGaN® FETs.

The EPC9113 wireless power system comprises the three boards (shown in Figure 1) namely:

• 1) A Source Board (Transmitter or Power Amplifier) EPC9509
  

• 2) A Class 3 A4WP compliant Source Coil (Transmit Coil)
  

• 3) A Category 3 A4WP compliant Device Coil with rectifier and DC smoothing capacitor.

The amplifier board features the enhancement-mode, half-bridge field effect transistor (FET), the 60 V rated EPC2108 eGaN FET with integrated synchronous bootstrap FET. 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 A4WP standard. This allows for testing compliant to the A4WP class 3 standard over a load range as high as ±50jΩ. The pre-regulator features the 100 V rated 65mΩ EPC2036 as the main switching device for a SEPIC converter.

The EPC9509 can operate in either Single ended or Differential mode by changing a jumper setting. This allows for high efficiency operation with load impedance ranges that allow for single ended operation. The timing, the timing adjust circuits for the ZVS class-D amplifiers have been separated to further ensure highest possible efficiency setting and includes separate ZVS tank circuits.

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, and maximum voltage. the coil current has the lowest priority followed by the power delivered with 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 all contribute to variations in coil current, DC power, and amplifier voltage requirements. Under any conditions, the controller will ensure the correct operating conditions for the ZVS class-D amplifier based on the A4WP standard. The pre-regulator can be bypassed to allow testing with custom control hardware. The board further allows easy access to critical measurement nodes that allow accurate power measurement instrumentation hookup. A simplified diagram of the amplifier board is given in Figure 2.

The Source and Device Coils are Alliance for Wireless Power (A4WP) compliant and have been pre-tuned to operate at 6.78 MHz with the EPC9509 amplifier. The source coil is class 3 and the device coil is category 3 compliant.

The device board includes a high frequency schottky diode based full bridge rectifier and output filter to deliver a filtered unregulated DC voltage. The device board comes equipped with two LED’s, one green to indicate the power is being received with an output voltage equal or greater than 4V and a second red LED that indicates that the output voltage has reached the maximum and is above 37V. GaN