ML4824 Datasheet, PDF (1/16 Pages) Fairchild Semiconductor – Power Factor Correction and PWM Controller Combo

December 2000
ML4824
Power Factor Correction and PWM Controller Combo
GENERAL DESCRIPTION
FEATURES
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
(f_PWM = f_PFC) and the ML4824-2 (f_PWM = 2 x f_PFC).
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 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.
s Internally synchronized PFC and PWM in one IC
s Low total harmonic distortion
s Reduces ripple current in the storage capacitor between
the PFC and PWM sections
s Average current, continuous boost leading edge PFC
s Fast transconductance error amp for voltage loop
s High efficiency trailing edge PWM can be configured
for current mode or voltage mode operation
s Average line voltage compensation with brownout
control
s PFC overvoltage comparator eliminates output
“runaway” due to load removal
s Current fed gain modulator for improved noise immunity
s Overvoltage protection, UVLO, and soft start
BLOCK DIAGRAM
16
VEAO
1
IEAO
VFB
15
2.5V
IAC
2
VRMS
4
ISENSE
3
VEA
–
+
3.5kΩ ^IEA
+
–
GAIN
MODULATOR
3.5kΩ
POWER FACTOR CORRECTOR
OVP
+
2.7V –
+
–
–1V +
–
PFC ILIMIT
VCCZ
13.5V
13
VCC
7.5V
REFERENCE
VREF
14
SQ
RQ
SQ
PFC OUT
12
RAMP 1
7
OSCILLATOR
RQ
RAMP 2
8
8V
x2
(-2 VERSION ONLY)
DUTY CYCLE
LIMIT
VDC
6
VCC
SS
5
50µA
8V
DC ILIMIT
9
1.25V
–
+
–
+
VIN OK
VFB –
1V –
2.5V +
+
DC ILIMIT
PULSE WIDTH MODULATOR
VCCZ
SQ
RQ
PWM OUT
11
UVLO
REV. 1.01 12/7/2000