LED Drivers
Most low current LEDs can usually be driven directly from integrated circuits as the normal operating current is in the region of 2-20mA. Because LEDs have a very similar forward voltage drop over a wide range of operating current, current limiting is important to maintain correct operating conditions. Often this will be a simple resistor, but high flux LEDs demand more sophisticated control.
High Current LED Drivers
Operating currents for illuminating LEDs can be in excess of 1A. In applications requiring multiple LEDs, it is mandatory to connect them in a series string. This ensures that operating currents and hence brightness and colour shade are well matched. To avoid significant power wastage, a switching converter operating in constant current output mode is needed. Buck or boost topologies can be used depending on the input voltage. Abacus can offer a large range of devices from National Semiconductor, ST Microelectronics and Texas Instruments, specifically designed for LED driving. Often, high flux LEDs are assembled into luminaires and the expected power source will be the mains. Integrated flyback converters can be successfully used to provide an isolated constant current output to drive series strings of LEDs. Both Power Integrations and ST Microelectronics offer solutions supporting the power levels commonly needed for LED luminaires.
If isolation is not required (ie. within a closed luminaire), the same parts may be used in a buck topology, reducing overall cost at the penalty of reduced efficiency. Abacus can also offer off the shelf solutions for mains powered converters from Osram LED Systems (LS) with universal inputs and DC outputs preset to 10 and 24V. Constant current versions are available with 350 and 700mA rating, capable of driving up to 12 series connected high power LEDs.
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LED Driver Selector Guides
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