Patent ID: 8040019

Claim:
An apparatus comprising: a switching node; a first transistor that is coupled to the switching node, wherein the first transistor has a control electrode; a second transistor that is coupled to the switching node, wherein the second transistor has a control electrode; a transducer that is coupled to the switching node; a gate driver that is coupled to control electrodes of the first and second transistors; a third transistor that is coupled to the switching node, wherein the third transistor has a control electrode; a comparator that is coupled to the third transistor and ground; a period detector that is coupled to the comparator; and a controller that is coupled to the gate driver, the control electrode of the third transistor, and the gate driver, wherein the controller controls the gate driver with a drive signal so as to drive the transducer with the first and second transistors in a first mode, and wherein the controller actuates the third transistor in a second mode so that the period detector measures the period of oscillation of the transducer, and wherein the controller adjusts the drive signal so as to generally match the natural frequency of the transducer.