300 Watt Class E Amplifier Using MRF151A
Modern industrial applications for high-efficiency, switch-mode RF amplifiers include laser, plasma, magnetic resonance imaging (MRI), and communications. The power levels and frequency of operation of industrial equipment used in these areas vary greatly. While plasma and heating applications tend to cluster at 13.56 MHz and 27.12MHz, laser and MRI applications tend to migrate towards 40 MHz, 80 MHz, and 128 MHz. Power levels span the gamut from a few watts to hundreds of kilowatts.
The stability, reliability, and low RDS-ON resistance of MACOM high frequency, RF, power MOSFETs make them suitable for switch-mode amplifier applications. The MRF product line, which includes RF power MOSFETS in the 1MHz-1GHz frequency range, has been a communication industry standard for more than 30 years. These devices are also used in many switch-mode amplifier applications and can yield much higher power and efficiency levels than specified in the traditional class AB designs. This application note presents a class E amplifier design based on MRF151A, a single ended power MOSFET, where it yields up to 300 watts at 81.36 MHz with better than 82% efficiency.
Class E amplifiers are well suited to industrial applications due to their simplicity and the high efficiency which can be obtained at a single frequency or over a narrow bandwidth. In this type of amplifier the power transistor operates as an on-off switch and, and in conjunction with the load network, it offsets the current and voltage waveforms in order to minimize power dissipation and maximize efficiency.