The SQ6601PT is a hybrid IC consists from power MOSFET and a controller IC, designed for Indirect feed-back Quasi-Resonant (including low frequency PRC)fly-back converter type SMPS (Switching Mode Power Supply) applications. this IC realizes high efficiency, low noise, downsizing and standardizing of a power supply system reducing external components count and simplifying the circuit designs. the device is provided in a five pin overmolded TO-220 style package, affording dielectric isolation without compromising thermal characteristics. (Note). PRC is abbreviation of "Pulse Ratio Control" (On-width control with fixed OFF-time).