Patent ID: 7715167

Claim:
A control unit for driving an alternating excitation current through an excitation coil of a magnetostrictive ultrasonic dental device and for setting the frequency thereof, the control unit comprising: a voltage-controlled oscillator for generating a variable frequency signal; a driver for setting up and regulating the excitation current according to said variable frequency signal; a current sensor in series with the excitation coil, to output a current-sense signal corresponding to the current flowing through the excitation coil; a function block operative to receive said current-sense signal and output a function signal proportional to a predetermined function thereof; an electrical arrangement receptive to said function signal and operative to continuously determine a value thereof; and a microprocessor for receiving said function signal and for controlling said voltage-controlled oscillator according to said function signal; wherein the excitation coil is not part of said voltage-controlled oscillator and is not connected directly to said voltage controlled oscillator and wherein said predetermined function of said current-sense signal contains a term proportional to the time-derivative of said current-sense signal.