Isolated Secondary-Side LED Lighting Dimmable Current Controller

The RT8457A is an isolated secondary LED current controller designed specifically for lighting fixtures such as E27, GU10, T5 and T8 that require power line isolation for safety and reliability, and that require high conversion efficiency as well as high LED current accuracy. The RT8457A contains 1) a constant current regulating amplifier with 170mV threshold used to program the LED string current with a simple resistor to within 5% LED current accuracy; 2) an over-voltage comparator to protect the output when LED string is open or broken; and 3) an opto-coupler driver to control the primary-side of the transformer to complete the system loop.

Precise dimming is achieved by controlling the LED current at the secondary-side via analog dimming. Applying a voltage greater than 1.1V at the ACTL pin will set the LED current sense threshold between the LED and GND pins at the highest level (around 170mV). The maximum LED current is adjustable by the sense resistor between the LED and GND pins. Lowering the ACTL pin voltage will reduce the LED current sense threshold.

The RT8457A is available in the SOP-8 package.