GENERAL DESCRIPTION

The ML4824 is a controller for power factor corrected, switched mode power supplies. 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 specification. The ML4824 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 ML4824-1 (fPWM = fPFC) and the ML4824-2 (fPWM = 2 x fPFC). Doubling the switching frequency of the PWM allows the user to design with smaller output components while maintaining the best operating frequency for the PFC. 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 brownout protection. The PWM section can be operated in current or voltage mode at up to 250kHz and includes a duty cycle limit to prevent transformer saturation.

FEATURES

■ Internally synchronized PFC and PWM in one IC

■ Low total harmonic distortion

■ Reduces ripple current in the storage capacitor between

the PFC and PWM sections

■ Average current, continuous boost leading edge PFC

■ Fast transconductance error amp for voltage loop

■ High efficiency trailing edge PWM can be configured

for current mode or voltage mode operation

■ Average line voltage compensation with brownout

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