Abstract: In order to achieve high system efficiency, optimized bus voltage and electrolytic capacitor-free in both high-line and low-line conditions, a flexible mode LED driver was proposed. A bidirectional switch was added and the LED driver could work in suitable mode. When the line voltage was within the range of 220240 V, the bidirectional switch was turned off and the proposed topology works in half voltage input mode（HVIM）, the high input voltage was divided equally by the input capacitors and the boost inductor works in boundary conduction mode（BCM）. When the line voltage was within the range of 100-120 Vrms, the bidirectional switch was turned on and the proposed topology works in full voltage input mode（FVIM）, the voltage of the input capacitors equals to the input voltage and the boost inductor works in discontinuous conduction mode（DCM）. Meanwhile, ZVS characteristic of the active switches can be fulfilled in both modes. The detail structure, operational principle and design considerations are examined in detail. Finally, the feasibility and the effectiveness of the proposed LED driver are verified by an experimental prototype with rated power of 100 W.