GENERAL DESCRIPTION
The ML4827 is a controller for power factor corrected, switched mode power supplies, that includes circuitry necessary for conformance to the safety requirements of UL1950. A direct descendent of the industry-standard ML4824-1, the ML4827 adds a TriFault Detect™ function to guarantee that no unsafe conditions may result from single component failure in the PFC. 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 IEC1000-3-2 specification. The ML4827 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 device is available in two versions; the ML4827-1 (Duty CycleMAX = 50%) and the ML4827-2 (Duty CycleMAX = 74%). The higher maximum duty cycle of the -2 allows enhanced utilization of a given transformer core’s power handling capacity. An over voltage 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 brown out protection. The PWM section can be operated in current or voltage mode, and includes a duty cycle limit to prevent transformer saturation.

FEATURES
■ Pin-compatible with industry-standard ML4824-1
■ TriFault Detect™ to conform to UL1950™ requirements
■ Available in 50% or 74% max duty cycle versions
■ 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 can be configured for current mode or voltage mode operation
■ Average line voltage compensation with brown-out control
■ PFC overvoltage comparator eliminates output “runaway” due to load removal
■ Current fed gain modulator for improved noise immunity
■ Overvoltage protection, UVLO, and soft start