A group of novel power conversion concept is developed with this invention for LED and OLED drive applications. The concept utilizes a single power conversion stage to fulfill multiple functions, including Power Factor Correction, DC voltage to DC current conversion, or DC voltage to DC voltage conversion etc. that are necessary for driving LED devices from an AC power input. Multiple dimming control schemes have also been developed to facilitate wide range of application requirements and enable the system to work with different input power format including AC mains power and variable AC voltage from the existing AC dimmer installations.