A half-bridge (HB) resonant inverter for driving a cold cathode fluorescent lamp (CCFL) backlight module with a piezoelectric transformer (PT) is analyzed in this paper. The resonant inductance of the HB inverter is expressed as a function of the load current, the load resistance the PT circuit parameters. Also, the trans-admittance of the PT-CCFL combination network is measured to track the resonant frequency of the PT which may be varied due to the temperature rise. The efficiency of the HB resonant inverter, the output power of the PT and the CCFL driving current are thus remained almost constant. Experiments show that the observed results match the theoretical analyses.