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ML4841
Variable Feedforward PFC/PWM Controller Combo

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 mode, boost type, 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 multiplier for improved noise immunity Overvoltage protection, UVLO, and soft start

General Description
The ML4841 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 specifications. The ML4841 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 ML4841 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 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.

Block Diagram
16 VEAO VFB 15 2.5V IAC 2 VRMS 4 ISENSE 3 RAMP 1 8 RTCT 7 RAMP 2 9 8V VDC 6 VCC SS 5 8V 50 A 1.25V

1 IEAO POWER FACTOR CORRECTOR OVP
-

13 VCC VCCZ 13.5V 7.5V REFERENCE S -1V
-

VEA

VREF 14

3.5k
-

IEA 2.7V

-

Q

GAIN MODULATOR 3.5k

8V

R S

Q PFC OUT Q 12

PFC ILIMIT

R

Q

OSCILLATOR

2 DUTY CYCLE LIMIT

PWM OUT S VFB 2.5V

Q

VIN OK

11

R DC ILIMIT

Q

1V

-

PULSE WIDTH MODULATOR

VCCZ

UVLO

REV. 1.0.3 6/13/01

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ML4841 DATASHEET