ML4841 Datasheet, PDF (1/15 Pages) Fairchild Semiconductor – Variable Feedforward PFC/PWM Controller Combo

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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 compara-
tor 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
1
IEAO
POWER FACTOR CORRECTOR
VFB
15
VEA
-
3.5kΩ ^IEA
2.5V +
-
+
IAC
+
-
2
VRMS
4
ISENSE
GAIN
MODULATOR
8V
3.5kΩ
3
RAMP 1
8
RTCT
7
OSCILLATOR
÷2
2.7V
OVP
+
-
-1V +
-
PFC ILIMIT
VCCZ
13.5V
13
VCC
7.5V
REFERENCE
VREF
14
SQ
RQ
SQ
PFC OUT
12
RQ
RAMP 2
9
8V
VDC
6
VCC
1.25V
SS
5
50µA
8V
-
+
-
+
DUTY CYCLE
LIMIT
VIN OK
VFB
-
+
2.5V +
1V -
DC ILIMIT
SQ
RQ
PWM OUT
11
PULSE WIDTH MODULATOR
VCCZ
UVLO
REV. 1.0.3 6/13/01