Resonant charging – wireless power transfer
User-friendliness and the ability to charge multiple devices at the same time
Resonant wireless charging provides a range of benefits including enhanced user-friendliness – you can place a device anywhere in the vicinity of the transmitter (usually with up to 30 mm of vertical freedom) – and the ability to charge multiple devices of varying sizes and power at the same time. It is operating at 6.78 MHz and the standard is driven by the AirFuel Alliance. Resonant wireless charging systems communicate using Bluetooth Low Energy, while proprietary resonant solutions utilize in-band communication. Two main topologies can be used to develop resonant solutions: Class-D (full-bridge or half-bridge) topology and class-E (single-ended or differential) topology.
Resonant wireless charging operates at very high frequencies. This creates significant challenges for standard silicon power technologies in transmitter and receiver devices, especially in higher power designs. Class-D zero voltage switching (ZVS) and differential class-E are the main topologies used for resonant wireless charging systems. Both approaches reduce switching losses by transitioning between the on- and off-switching positions of power devices at zero volt across the respective power switch.
Class-D topologies can use a half or full bridge with a bus voltage under 100 V, whereby the switching nodes switch between zero volts and the bus voltage. The circuit is tuned for zero voltage switching over the required range of output impedance. In the Class-D ZVS topology, lower breakdown voltage devices can be used to increase overall system efficiency.
Class-E topologies have single-switch and dual-switch differential options. In each case, the drain is connected to the resonant circuit. When correctly tuned for zero-voltage switching with no body diode conduction, the drain voltage peaks at 3.56 times the DC bus voltage. Under non-ideal conditions, the drain voltage may rise much higher. A simpler driver architecture (low-side only) and a single switch per Class-E branch can help reduce system costs.
CoolGaN™ is ideally suited to both topologies as it can maximize overall system performance (in class-D implementations) and also reduce overall system solution costs (in class-E implementations). Due to its significantly reduced parasitic capacitances, CoolGaN™ is the ideal choice when switching at frequencies in the MHz range (e.g. 6.78 MHz); it provides low, almost linear, COSS without a large increase at low VDS, enabling ZVS over a wide load impedance range. In addition, CoolGaN™ offers very low QG and QOSS compared with equivalent silicon MOSFETs, which, together with the Driver IC, helps switch power faster.
Webinar: Challenges and design considerations for next generation wireless power systems
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|Spark Connected is a product development and engineering solutions company delivering high technology in wireless power systems and battery management solutions. Spark Connected provides full system level wireless power solutions in both standards based and proprietary Inductive as well as proprietary Resonant technologies.||Americas, Asia-Pacific, Europe, Middle East, Africa, Greater China, Japan||Power, Microcontroller||Software, Hardware, Services||Full system level wireless power solutions. Software based intelligent control systems. Hardware receiver and transmitter architectures and design files. Design custom coils for non-standard applications and form factors. Support customers Integrate Spark Connected solutions into End-Products. Support Regulatory and Safety standards|