The LM3444 is an adaptive constant off-time AC/DC buck (step-down) constant current controller that provides a constant current for illuminating high power LEDs. The high-frequency capable architecture allows the use of small external passive components. A passive PFC circuit ensures good power factor by drawing current directly from the line for most of the cycle, and provides a constant positive voltage to the buck regulator. Additional features include thermal shutdown, current limit and VCC undervoltage lockout. The LM3444 is available in a low profile 10-pin VSSOP package or an 8-lead SOIC package.