A driver comprises a front-end stage, a back-end stage, and an intermediate controller. The front-end stage comprises a front-end main circuit and a front-end controller, and is configured to rectify an AC input voltage from an external power supply and output a DC bus voltage through output terminals. The back-end stage comprises a buck circuit, and configured to receive the bus voltage from the front-end stage and output a desired DC drive voltage to a load according to an operating voltage of the load. The intermediate controller is configured to obtain a difference voltage signal indicative of an electric potential difference between the bus voltage and the drive voltage, and provide a feedback signal generated based on the difference voltage signal to the front-end controller. The front-end controller controls the front-end main circuit based on the feedback signal to change the bus voltage with change of the drive voltage.