A drive for a phacoemulsification probe includes a drive circuit for supplying electrical power to the probe, circuitry for sensing the electrical power supplied by the drive circuit to the probe and for supplying electrical signals indicative of the magnitude of the electrical power supplied. A manually operable input device provides a signal indicative of the transducer power level desired by the user of the probe. A control circuit is responsive to the signal indicative of the desired transducer power level and to the signals indicative of the magnitude of the supplied electrical power for providing control signals to the drive circuit to control the power applied in an efficient manner. The drive circuit includes a totem-pole switch, responsive to at least one of the control signals, to apply power in a square-wave waveform, and a switching regulator for supplying a supply voltage to the totem-pole switch. The totem-pole switch has circuitry associated therewith which is responsive to one of the control signals to initially vary the frequency of the square-wave waveform. The regulator is responsive to a second control signal from the control circuit to vary the voltage supplied by the regulator to the totem-pole switch to control the amplitude of the square-wave waveform. The switching nature of this system substantially minimizes the power consumption of the drive circuit as compared with conventional techniques.