Enhanced Off line Switcher for Robust and Highly Efficient Power Supplies

The NCP1079A & NCP1079B products integrate a fixed frequency current mode controller with a 700 V MOSFET. Available in a two different pin out of the very common PDIP 7 package, it offers a high level of integration, including soft start, frequency jittering, short circuit protection, skip cycle, a maximum peak current set point, ramp compensation, and a dynamic self supply (DSS, eliminating the need for an auxiliary winding). Unlike other monolithic solutions, the NCP1079A & NCP1079B is quiet by nature: during nominal load operation, the part switches at one of the available frequencies (65 or 100 kHz). When the output power demand diminishes, the IC automatically enters frequency foldback mode and provides excellent efficiency at light loads. When the power demand reduces further, it enters into a skip mode to reduce the standby consumption down to a no load condition. Protection features include: a timer to detect an overload or a short circuit event, Over voltage Protection with auto recovery. Ac input line voltage detection prevents lethal runaway in low input voltage conditions (Brown-out) as well as too high an input line (Ac line Over voltage Protection). This also allows an Over power Protection to compensate all internal delays in high input voltage conditions and optimize the maximum output current capability. For improved standby performance, the connection of an auxiliary winding stops the DSS operation and helps to reduce input power consumption below 50 mW at high line.