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

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.
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.
s Internally synchronized PFC and PWM in one IC
s Low total harmonic distortion
s Reduced ripple current in the storage capacitor
between the PFC and PWM sections
s Average current, continuous boost, leading edge PFC
s High efficiency trailing edge PWM with dual
totem-pole outputs
s Average line voltage compensation with brown-out
control
s PFC overvoltage comparator eliminates output
“runaway” due to load removal
s Current-fed multiplier for improved noise immunity
s Overvoltage protection, UVLO, and soft start
BLOCK DIAGRAM
* This Part Is End Of Life As Of August 1, 2000
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
RAMP 2
9
8V
VDC
6
VCC
SS
5
50µA
8V
DC ILIMIT
10
1.5V
OSCILLATOR
x2
(-2 VERSION ONLY)
DUTY CYCLE
LIMIT
-
+
-
+
VIN OK
VFB
-
1V -
2.5V +
+
DC ILIMIT
PULSE WIDTH MODULATOR
VCCZ
SQ
TQ
SQ
RQ
UVLO
VCC2
16
PWM 2
14
PGND
VCC2
PWM 1
13
PGND
12
1