This document is an engineering report describing an isolated power factor dimmable LED driver (power supply) using the LYT4314E from the LYTSwitch family of devices. The DER-366 provides a single 20W (36 VTYPICAL) dimmable constant 550 mA current output over an input voltage range of 190 to 265 VAC. Key design goals are high efficiency to maximize efficacy and small size. This allows the driver to be installed into a PAR38 sized lamp as close as possible to the production design.