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  • Offline LED Driver

  • Created: Feb 17, 2016

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This design is a simple nonisolated LED driver that is intended to operate directly from a 400VDC input. It can basically drive a string of 27 white LEDs or 6 amber LEDs at 400mA. It uses the MAX16801 high brightness LED driver control that is well suited for universal input (rectified 85VAC to 265VAC) LED drivers. It features an input undervoltage lockout (UVLO) for programming the input-supply start voltage, and to ensure proper operation during brownout conditions and has has an internal-bootstrap undervoltage lockout circuit with a large hysteresis that simplifies offline LED driver designs.

The circuit is a flyback LED driver that can drive multiple LEDs in series at 400mA. With the jumper installed, the design drives 6 amber LEDs at 400mA. The design uses the MAX16801 HB LED controller and a three-winding transformer. The transformer has an 18:6:1 turns ratio where its primary inductance is 800µH with a current rating of 750mA (peak) and a duty cycle always less than 50%. The switching MOSFET has an isolated tab, which allows the heatsink to be connected to ground. This minimizes the metallic surface area that experiences high-speed voltage transients, and, in turn, minimizes radiated EMI.

This offline LED driver is useful in general lighting and display applications. This may be used in commercial, decorative, architectural and industrial lighting. In addition, offline LED drivers are also used for street lighting and public illumination as well as emergency and residential lighting.



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