Single-ended compact MOSFET power inverter with automatic frequency control for maximizing RF output power in megasonic transducer at 3 MHz

A single-ended compact MOSFET DC-to-RF power inverter is built to drive a megasonic transducer having an impedance of as low as 5 to 6 ohms or less at 3 MHz. The operating frequency of the MOSFET DC-to-RF power inverter is automatically set at the resonating frequency of the megasonic transducer using the PLL, so that the RF power in the megasonic transducer is maximized. The impedance of the inverter load consisting of an output transformer, a matching capacitor, a coaxial cable, a megasonic transducer, and a current sensor is calculated to determine the frequency control range of the PLL. In accordance with the result of calculation, the performance of the PLL consisting of a phase-frequency comparator, a low-pass filter, and a VCO is determined. The output power of the single-ended compact MOSFET power inverter was 25 W with a power conversion efficiency of 70%, when the operating frequency was set at the resonating frequency of the megasonic transducer.