Operating frequency control for maximizing output power of MOS-FET power inverter to drive megasonic transducer at 3 MHz

The operating frequency of the MOSFET DC-to-RF power inverter is controlled using the PLL when the MOSFET DC-to-RF power inverter is used to drive a megasonic transducer having an impedance of as low as 2 to 3 ohms or less. The impedance of the inverter load (composed of the output transducer, matching capacitor, coaxial cable, megasonic transducer and current sensor) is calculated to determine the frequency control range of the PLL. In accordance with the results of calculations, the performance of the phase-frequency comparator, lowpass filter and VCO is decided. When the output power of the MOSFET power inverter was 60 W with a power conversion efficiency of 95%, the frequency control range was 2.8 MHz to 3.2 MHz. The PLL covers the range of frequency shifts and variations in the megasonic transducer and VCO devices used in the system