A novel single switch dc converter based on resonant passive switch module (RPSM) is proposed for dimmable LED drivers to attain wide duty ratio operating range. Utilizing the proposed RPSM, the output ripple can be reduced by connecting the inductor in series with LED and adopting a capacitive voltage divider. The proposed driver can automatically balance the forward voltage drop of LEDs because of the variable structure characteristics of the proposed RPSM; therefore, the energy can be transferred to the output without an energy barrier existing in the conventional dc converters. The achievable duty ratio operating range of the proposed LED driver can thus be widened, consequently increase the dimming levels for both digital and analog controllers. In addition, dual PWM dimming can be realized easily using the proposed technique. In summary, the distinctive features and simple circuit of the proposed converter make it suitable for realizing the digital dimmable LED driver. Finally, a compact prototype for LED AR111 lamps is constructed using SMT components to manifest the effectiveness of the proposed driver through a low switching frequency of 100kHz.