Control circuit for piezoelectric ultrasonic generators

Abstract

A high power ultrasonic generator for driving a transducer/horn assembly includes a transistor bridge inverter power output circuit connected to a DC source for producing an alternating output current. A pulse generating circuit produces a bipolar train of pulses for controlling the switching of the transistors in the bridge inverter circuit. The pulse widths are adjusted to provide a dead time therebetween at least equal to the storage time of the inverter transistors to prevent any overlap in the conduction of the opposite legs thereof. Overload control means reduces the widths of the pulses when the output current exceeds predetermined levels, thereby to reduce the output current. A starting circuit in the pulse generator gradually increases the pulse widths during start-up of the generator, and other circuitry protects against unduly high current loads in the power supply during AC turn-on of the system. The pulse generating circuit also includes a phase locked loop oscillatory circuit having an input connected through a bandpass feedback amplifier to the power output circuit for synchronizing the pulse generating circuit to the frequency of operation of the transducer/horn assembly, the bandpass amplifier being selectively tunable for use with different horns.