This paper presents a two-stage PFC LED driver. The two outstanding features of the proposed driver are: 1) the entire system has no electrolytic capacitor, which prolongs the lifetime of the LED driver; 2) LED string current is controlled directly and PWM dimming is also provided. This makes the driver virtually a current source driver. The front end stage is the conventional Boost AC/DC converter which provides a PFC (power factor correction) function and operates on the Critical Conduction Mode (CRM). The cascaded DC/DC converter is an LLC resonant converter. The operations and the choice of the capacitors are studied in this paper. Experimental results are presented to verify the theoretical predictions.