June 1998
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).
■ 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 boost leading edge PFC
■ Fast transconductance error amp for voltage loop
The device is available in two versions; the ML4824-1
(f
PWM
= f ) and the ML4824-2 (f
= 2 x f ).
■ High efficiency trailing edge PWM can be configured
PFC
PWM
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.
for current mode or voltage mode operation
■ Average line voltage compensation with brownout
control
■ PFC overvoltage comparator eliminates output
“runaway” due to load removal
■ Current fed gain modulator for improved noise immunity
■ Overvoltage protection, UVLO, and soft start
BLOCK DIAGRAM
*Some Packages Are Obsolete
16
1
13
POWER FACTOR CORRECTOR
V
CC
IEAO
VEAO
V
CCZ
OVP
V
V
REF
VEA
FB
13.5V
7.5V
REFERENCE
+
IEA
14
12
3.5kΩ
15
–
+
–
2.7V
–1V
–
+
–
2.5V
AC
+
S
Q
I
2
4
3
+
–
GAIN
V
R
S
Q
Q
RMS
MODULATOR
PFC OUT
3.5kΩ
PFC I
LIMIT
I
SENSE
R
Q
RAMP 1
OSCILLATOR
7
8
x 2
(-2 VERSION ONLY)
RAMP 2
DUTY CYCLE
LIMIT
8V
–
+
V
1.25V
DC
6
5
9
PWM OUT
V
S
Q
Q
CC
11
–
+
V
OK
1V
IN
V
–
50µA
8V
FB
SS
–
+
R
2.5V
+
DC I
LIMIT
DC I
LIMIT
V
UVLO
CCZ
PULSE WIDTH MODULATOR
1