| The Class-E amplifier is a switching-mode amplifier in which the transistor operates as a switch with a passive, resonant load network. Losses are minimized by having the transistor switch on when both the voltage and current are small. These amplifiers are extremely efficient with about 90% of the DC input power converted to RF output power. This thesis will present two high-power Class-E amplifiers designed for the Industrial, Scientific, and Medical (ISM) frequency of 13.56 MHz. The first is a 200-W amplifier that incorporates the inexpensive International Rectifier IRFP440 MOSFET. With a drive level of 10 W, a drain efficiency of 91% and an overall efficiency of 87% are achieved. The second is a 400-W, air-cooled design that uses a new International Rectifier low-charge MOSFET, the IRFP450LC. This device features improved switching speed and reduced gate drive requirements. A drive level of 12 W is used to attain a drain efficiency of 86% and an overall efficiency of 84%. In both amplifiers, all harmonics are more than 40dB below the carrier. Design procedures, modelling techniques, and extensive experimental results will be presented for each. In addition, results from a thermal study of a 400-W Class-E amplifier will be discussed. Component and junction temperature data are obtained by a direct measurement technique, Infrared Thermographic Imaging or Thermography and compared with simulated results. Particular attention is paid to the MOSFET and load network capacitors. |
