with Keith Szolusha Senior Applications Engineer, Power Products

LEDs are becoming both more popular and more powerful. Strings of 1A, 2A, 3A and higher current LEDs found in vehicles, billboards, industrial lighting, and many more applications need to be driven both accurately and efficiently from DC/DC converters. In many cases, a step-up and step-down topology is needed due to the voltage variation of both the LED string and the input source. In this case, a 4-switch synchronous buck-boost controller is the best solution for its efficiency and small circuit size.

Linear Technology’s LT®3791 is a buck-boost controller IC that drives LED strings from an input voltage up to 60V to an output voltage up to 60V. It can drive over 100W of LEDs at over 98% efficiency. It smoothly transitions from buck region to buck-boost region to boost region as the relationship between input and output voltage changes. LTCs high-end PWM dimming provides accurate and deep brightness control to the LEDs. Short-circuit and open LED string protection and diagnostics make this a robust and highly useful step-up/step-down LED driver.

The LT3791 can operate as both a constant current and constant voltage DC regulator, so it can also be used as an excellent high power buck-boost voltage regulator up to 60V and with short-circuit protection. Both constant current and constant voltage are needed for special sealed lead acid battery chargers and LT3791 has a special 1/10th charger current detection that can be used to switch from a charge voltage to a float voltage for a charged up high power SLA battery.