Automotive light-emitting-diode (LED) drivers require special design considerations, which includes voltage step-up and step-down function, high energy efficiency, and fast current reference tracking capability. Unlike the conventional efficiency improvement methods, which is based on cumbersome circuit/component optimization and/or modification for a single operating point, this paper proposes a simple approach based on topology transition which can achieve a high efficiency for a wide input voltage range. In particular, the topology of the LED driver can change between buck, boost, and buck-boost converter according to the level of the input voltage. In addition, a novel current mode controller is proposed, such that 1) compatibility to different topologies, 2) seamless topology transition, and 3) fast current reference tracking can be concurrently achieved. The feasibilities of the proposed topology transition method and its control has been experimentally verified through a four-switch buck-boost converter prototype with 7-45 V input, 25 V/1 A LED strings output. It is shown that there is more than 5% efficiency improvement as compared to the conventional four-switch buck-boost converter. Full range (0%-100%) and precise (1% dimming precision) pulse-width-modulated dimming has also been demonstrated.