In this paper, a novel single switch dc converter based on a resonant passive switch module (RPSM) is proposed for dimmable LED drivers to achieve lower output voltage ripple, higher efficiency and wide duty ratio operating range as well as a more compact size. Due to the variable structure characteristics of the proposed RPSM, not only the energy storage elements can be coordinated with the output capacitor to reduce output ripple, but also the forward voltage drop of LEDs can be cancelled automatically, so that the energy can be transferred to the output without the energy barrier which exists in traditional dc converters. The operating principle and theoretical analysis of the proposed converter are then presented, and some design guidelines are also provided. Finally, a compact prototype for LED AR111 lamps is also constructed using only SMT components to demonstrate the correctness and effectiveness of the proposed LED driver.