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

May 1997
ML4841*
Variable Feedforward PFC/PWM Controller Combo
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.
FEATURES
s Internally synchronized PFC and PWM in one IC
s Low total harmonic distortion
s Reduced ripple current in the storage capacitor
between the PFC and PWM sections
s Average current, continuous mode, boost type,
leading edge PFC
s High efficiency trailing edge PWM can be configured
for current mode or voltage mode operation
s Average line voltage compensation with brown-out
control
s PFC overvoltage comparator eliminates output
“runaway” due to load removal
s Current-fed multiplier for improved noise immunity
s Overvoltage protection, UVLO, and soft start
BLOCK DIAGRAM
*Some Packages Are End Of Life Or Obsoete
16
VEAO
1
IEAO
VFB
15
2.5V
IAC
2
VRMS
4
ISENSE
3
RAMP 1
8
VEA
-
+
3.5kΩ ^IEA
-
+
GAIN
MODULATOR
8V
3.5kΩ
POWER FACTOR CORRECTOR
OVP
+
2.7V -
+
-
-1V +
-
PFC ILIMIT
VCCZ
13.5V
13
VCC
7.5V
REFERENCE
VREF
14
SQ
RQ
SQ
RQ
PFC OUT
12
RTCT
7
OSCILLATOR
÷2
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
1