An inverter includes a plurality of switching elements that convert between DC and AC power. The method includes providing a bone fastener depending from the head portion, arranging the spinal rod in the channel of the head portion, and providing a locking cap having first and second portions that are rotatable relative to one another, the second portion of the locking cap having an underside with a recess. The controller controls an output voltage according to each power state of a processor operating in a transition state where a power state of the processor transitions between an active state and a predetermined sleeping state at a predetermined transition frequency.