Megasonic transducer drive utilizing MOSFET DC-to-RF inverter with output power of 600 W at 1 MHz

This paper describes MOSFET power inverter systems, each provided to drive a megasonic transducer with an output power of 600 W at a frequency of 1 MHz. Since the megasonic transducer is used as a resonant load with a series resistance of approximately 1 /spl Omega/, the impedance characteristic of the megasonic transducer used as an inverter load is analyzed and compared with measured data. A new method is developed to match the inverter output impedance to the load impedance of as low as 1 /spl Omega/ at the resonant frequency using a high-performance output transformer which can feed RF power to the load at high efficiency. The output transformer having a primary-to-secondary winding ratio of 2 to 1 was used by the inverter to drive the megasonic transducer. Based on the analysis of the impedance characteristics of the load, two types of MOSFET dc-to-RF power inverters, a full-bridge version and a single-ended version, were designed and built. These power inverters were put into practical use in cleaners. The power conversion efficiency was greater than 80% for the full-bridge version at an output of approximately 600 W and 50% for the single-ended version at an output power of approximately 600 W. When the megasonic transducer was operated with an input power of 600 W. the operation was satisfactory.