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ML4826
PFC and Dual Output PWM Controller Combo
Features
Internally synchronized PFC and PWM in one IC Low total harmonic distortion Low ripple current in the storage capacitor between the PFC and PWM sections Average current, continuous boost, leading edge PFC High efficiency trailing edge PWM with dual totem-pole outputs 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 ML4826 is a high power controller for power factor corrected, switched mode power supplies. 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 specifications. The ML4826 includes circuits for the implementation of a leading edge, average current "boost" type power factor correction and a trailing edge, pulse width modulator (PWM) with dual totem-pole outputs. 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 at up to 250kHz and includes a duty cycle limit to prevent transformer saturation.

Block Diagram
20 VEAO VFB 19 2.5V IAC 2 VRMS 4 ISENSE 3 RAMP 1 8 RTCT 7 RAMP 2 9 8V VDC 6 VCC SS 5 8V DC ILIMIT 10 PULSE WIDTH MODULATOR VCCZ UVLO 50 A 1.5V

11 AGND IEAO

1 POWER FACTOR CORRECTOR OVP
-

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

VEA

VREF 18

3.5k
-

IEA 2.7V

-

Q

GAIN MODULATOR 3.5k

8V

R S

Q PFC OUT Q 15

PFC ILIMIT

R

Q

OSCILLATOR VCC2 DUTY CYCLE LIMIT S Q PWM 2 T Q PGND S VFB 2.5V

16 14

Q

VIN OK 1V

VCC2 PWM 1 13 PGND 12

R DC ILIMIT

Q

REV. 1.0.5 2/14/02

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ML4826-2 DATASHEET