June 1997
ML4826*
PFC and Dual Output PWM Controller Combo
GENERAL DESCRIPTION
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.
The device is available in two versions; the ML4826-1
(f
PWM
= f
PFC
) and the ML4826-2 (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 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.
FEATURES
s
s
s
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
totem-pole outputs
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
s
s
s
s
s
s
BLOCK DIAGRAM
20
VEAO
VFB
19
2.5V
IAC
2
VRMS
4
ISENSE
3
RAMP 1
8
RTCT
7
RAMP 2
9
8V
VDC
6
VCC
SS
5
8V
DC ILIMIT
10
50µA
1.5V
-
+
-
+
-
+
+
-
* This Part Is End Of Life As Of August 1, 2000
1
AGND
IEAO
POWER FACTOR CORRECTOR
OVP
+
+
11
17
VCCZ
13.5V
VCC
7.5V
REFERENCE
S
-1V
+
-
VEA
3.5kΩ
-
IEA
2.7V
VREF
18
-
Q
Q
PFC OUT
Q
Q
15
GAIN
MODULATOR
3.5kΩ
8V
R
S
R
PFC ILIMIT
OSCILLATOR
(-2 VERSION ONLY)
x2
DUTY CYCLE
LIMIT
S
T
Q
PWM 2
Q
PGND
S
VFB
2.5V
-
+
VCC2
16
14
Q
Q
VIN OK
1V
-
+
VCC2
PWM 1
13
PGND
12
R
DC ILIMIT
PULSE WIDTH MODULATOR
VCCZ
UVLO
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
