June 1997
ML4826*
PFC and Dual Output PWM Controller Combo
GENERAL DESCRIPTION
FEATURES
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.
■ Internally synchronized PFC and PWM in one IC
■ Low total harmonic distortion
■ Reduced 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
The device is available in two versions; the ML4826-1
totem-pole outputs
(f
= f ) and the ML4826-2 (f
= 2 x f ).
PWM
PFC
PWM PFC
Doubling the switching frequency of the PWM 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. 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.
■ 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
BLOCK DIAGRAM
* This Part Is End Of Life As Of August 1, 2000
20
11
1
17
POWER FACTOR CORRECTOR
V
CC
AGND
IEAO
VEAO
V
CCZ
OVP
V
V
REF
VEA
FB
13.5V
7.5V
REFERENCE
+
IEA
18
15
3.5kΩ
19
-
-
2.7V
-1V
-
+
-
2.5V
AC
+
+
S
Q
I
2
4
3
+
-
8V
GAIN
V
I
R
S
Q
Q
RMS
MODULATOR
PFC OUT
3.5kΩ
PFC I
LIMIT
SENSE
RAMP 1
R
Q
8
7
R C
T T
OSCILLATOR
V
CC2
x 2
(-2 VERSION ONLY)
RAMP 2
16
14
S
Q
DUTY CYCLE
LIMIT
9
PWM 2
8V
T
Q
-
V
PGND
1.5V
DC
6
5
+
V
S
Q
Q
CC
V
CC2
-
V
OK
1V
IN
PWM 1
PGND
V
-
50µA
8V
FB
SS
+
-
13
12
R
2.5V
+
+
DC I
LIMIT
V
DC I
LIMIT
10
UVLO
CCZ
PULSE WIDTH MODULATOR
1