A resonant DC/AC inverter includes a DC power source providing a DC voltage, a half-bridge power switch circuit electrically connected to the DC power source being operative to convert the DC voltage to an AC voltage, a resonant tank electrically connected between an output of the half-bridge power switch circuit and an input of a load being operative to boost and filter the AC voltage to generate an AC power voltage supplied to the load, and a controller being operative to detect a magnitude of current in the load and a magnitude of a voltage across the load and to generate pulse waveforms for turning on and off the half-bridge power switch circuit, wherein the controller substantially instantaneously varies a frequency of the pulse waveforms and a duty cycle of the pulse waveforms so as to operate the resonant DC/AC inverter near a neighborhood of a resonant frequency of the resonant tank regardless of a conduction state of the load and improve the efficiency of the inverter regardless of the higher DC voltage applied to the inverter. Particularly, the resonant DC/AC inverter utilizes a piezoelectric transformer to supply power to a fluorescent lamp which is wildly employed in display panels and is extensively used to provide backlighting for liquid crystal displays (LCDs), especially for backlighting LCD monitors and LCD televisions.