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.