An inverter includes a counter, a PWM generator, a central controller and a power converter. The counter is used for receiving a frame switch signal to generate a frame counting signal. The PWM generator is coupled to the counter, and is used to select a specific frequency among a plurality of predetermined frequencies according to the frame counting signal, and generate a modulated signal having the specific frequency. The central controller is coupled to the PWM generator, and is used to generate a processed signal according to the modulated signal. The power converter is coupled to the central controller, and is used to generate an output signal according to the processed signal.