The ZD850 is a constant off-time, high power LED driver IC using a Buck Converter Topology that is capable of driving up to 1.5A of output current. It operates from an input voltage range of 4VAC to 16VAC or 5VDC to 27VDC and generates a regulated programmable constant output current for high power LEDs. A patent pending design technique with AC/DC bridge rectifi er, linear regulator and internal high voltage NDMOS power switch has been designed on-chip to reduce component count by eliminating the need for an external power switch and diode bridge. Based on high effi cient PFM control design, the minimum Off-Time in the controlled frequency range is set at a typical 1.5μs, allowing a good LED current regulation over a wide range of supply voltage with LED voltages with respect to using conventional transformers or E-transformers. Built in thermal and overvoltage circuitry protects the power transistors from excessive power dissipation.