The present disclosure relates to a TFT-LCD and the driving circuit and the switching power supply thereof. The switching power supply includes a PWM controller, an electronic signal generator, and a field effect transistor. The output pins of the electronic signal generator being configured to output voltage signals that vary periodically between multiple voltage ranges. The frequency selection pins of the PWM controller and the output pins of the electronic signal generator are connected to receive the voltage signals from the electronic signal generator, and the PWM controller outputs switching signals of a predetermined frequency through at least one output pin according to a voltage range of the voltage signals received by the frequency selection pins. A gate pin of the FET connects to output pins of the PWM controller, and a source pin of the FET is grounded.