Resonant converter tuning for maintaining substantial constant phaco handpiece power under increased load

A phacoemulsification system comprising:

• a phacoemulsification handpiece including a cutting tip ultrasonically vibrated by an ultrasonic transducer;
• a power supply for driving said ultrasonic transducer at a resonant frequency of the transducer and cutting tip by phase shifting current supplied to the transducer.
• a resonant output circuit connected to the ultrasonic transducer and having an output voltage oscillating therethrough;
• a voltage sensor for providing a voltage signal corresponding to said output voltage;
• a bridge driver for controlling said resonant output circuit, said bridge driver being responsive to driver signals;
• control circuitry for producing an amplitude command in response to the voltage signals and a frequency command;
• and
• phase shift circuitry responsive to the frequency and amplitude commands for producing the driver signals by phase shifting the output voltage of one side of the bridge driver with respect to another side of the bridge circuit.