ML4826 Datasheet, PDF (1/16 Pages) Fairchild Semiconductor – PFC and Dual Output PWM Controller Combo

www.fairchildsemi.com
ML4826
PFC and Dual Output PWM Controller Combo
Features
• Internally synchronized PFC and PWM in one IC
• Low total harmonic distortion
• Low 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
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 specifi-
cations. The ML4826 includes circuits for the implementa-
tion of a leading edge, average current “boost” type power
factor correction and a trailing edge, pulse width modulator
(PWM) with dual totem-pole outputs.
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.
Block Diagram
20 11
VEAO
AGND
1
IEAO
VFB
19
2.5V
IAC
2
VRMS
4
ISENSE
3
VEA
-
+
3.5kΩ ^IEA
-
+
GAIN
MODULATOR
8V
3.5kΩ
POWER FACTOR CORRECTOR
OVP
+
2.7V -
+
-
-1V +
-
PFC ILIMIT
VCCZ
13.5V
17
VCC
7.5V
REFERENCE
VREF
18
SQ
RQ
SQ
PFC OUT
15
RAMP 1
8
RQ
RTCT
7
OSCILLATOR
VCC2
RAMP 2
9
8V
VDC
6
VCC
SS
5
50µA
8V
DC ILIMIT
10
1.5V
-
+
-
+
DUTY CYCLE
LIMIT
VIN OK
VFB
-
1V -
2.5V +
+
DC ILIMIT
PULSE WIDTH MODULATOR
VCCZ
SQ
TQ
SQ
RQ
UVLO
16
PWM 2
14
PGND
VCC2
PWM 1
13
PGND
12
REV. 1.0.5 2/14/02