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power transfer system teardown propagation delay and most importantly, greater than 50 V/ nsec dv/dt capability. The 2 x 2 mm micro SMD package allows efficient, common heat sinking of all power devices. Supporting the power plant are two Microchip low dropout regulators, MCP1703 5 MC in the 2 x 3 mm DFN package, chosen for the small size. The demo is quite flexible and allows the user to free run or synchronise to an external oscillator, and run open-loop or close it for a controlled output (using external circuitry). For self free running operation, the source board uses a CB3-3C-7M3728, 7.3728 MHz crystal oscillator to start up the system. Closing the loop requires a precision reference and ultrafast precision comparator. The LM4125AIM5-2.5 is a precision, low power low dropout reference from Texas Instruments. The comparator is a LT1016CS8, 10 nsec comparator capable of being run from a single 5V supply. The EPC9104 delivers 15W acros one inch of air at over 70% end-to-end eficiency The source and capture resonators are provided by WiTricity Corporation. These are high Q resonant circuits that are tuned to 6.78 MHz to maximise power transfer efficiency over distance, even when the magnetic coupling factor is low. Note that commercialisation of products using highly resonant wireless power transfer requires a license from WiTricity to its patent portfolio. The device board D consists of a simple rectifier bridge of PD3S140, 40-V Schottky rectifiers from Diodes, Inc. The rectifier is loaded by an array of jumper selectable resistor loads. Efficient Power Conversion, www.epc-co.com WiTricity, www.witricity.com C D Figure 3 The driver stage that produces the RF power waveform. VDS Abs. Max. 40 V VGS(TH) VDS = VGS = 2 mA 1.4 V (typ) RDS(ON) VGS = 5 V, ID = 10 A 16 mΩ (max) QG VDS = 20 V, VGS = 5 V ID = 10 A 2.48 nC (typ) QGD VDS = 20 V, ID = 10 A 0.48 nC QGS 0.67 nC QOSS VDS = 20 V, VGS = 0 V 4.8 nC Table 1 EPC2014 device key parameters w ww.edn-europe.com MARCH 2013 | EDN Europe 27


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