ML4801

November 1998 PRELIMINARY ML4801 Variable Feedforward PFC/PWM Controller Combo GENERAL DESCRIPTION The ML4801 is a controller for power factor corrected, switched mode power supplies. Key features of this combined PFC and PWM controller are low start-up and operating currents. Power Factor Correction (PFC) allows the use of smaller, lower cost bulk capacitors, reduces power line loading and stress on the switching FETs, and results in a power supply that fully complies with IEC1000-2-3 specifications. The ML4801 includes circuits for the implementation of a leading edge, average current “boost” type power factor correction and a trailing edge pulse width modulator (PWM). The PFC frequency of the ML4801 is automatically set at half that of the PWM frequency generated by the internal oscillator. This technique allows the user to design with smaller output components while maintaining the optimum operating frequency for the PFC. An overvoltage comparator shuts down the PFC section in the event of a sudden decrease in load. The PFC section also includes peak current limiting and input voltage brownout protection. FEATURES s s s s s Internally synchronized PFC and PWM in one IC Low start-up current (200µA typ.) Low operating current (5.5mA typ.) Low total harmonic distortion Reduces ripple current in the storage capacitor between the PFC and PWM sections Average current continuous boost leading edge PFC High efficiency trailing edge PWM optimized for current mode operation Curr...