ML4821 Datasheet, PDF (1/12 Pages) Fairchild Semiconductor – Power Factor Controller

ML4821
Power Factor Controller
www.fairchildsemi.com
Features
• Average current sensing for lowest possible harmonic
distortion
• Average line compensation with brown-out control
• Precision buffered 5V reference
• 1A peak current totem-pole output drive
• Overvoltage comparator eliminates output “runaway” due
to load removal
• Wide common mode range in current sense comparators
for better noise immunity
• Large oscillator amplitude for better noise immunity
• Output driver internally limited to 17V
• “Sleep mode” shutdown input
Block Diagram
General Description
The ML4821 provides complete control for a “boost” type
power factor correction system using the average current
sensing method. Special care has been taken in the design of
the ML4821 to increase system noise immunity. The circuit
includes a precision reference, gain modulator, average
current error amplifier, output error amplifier, over-voltage
protection comparator, shutdown logic, as well as a high
current output. In addition, start-up is simplified by an under-
voltage lockout circuit.
In a typical application, the ML4821 controls the AC input
current by adjusting the pulse width of the output MOSFET.
This modulates the line current so that its shape conforms to
the shape of the input voltage. The reference for the current
regulator is a product of the sinusoidal line voltage times the
output of the error amplifier which is regulating the output
DC voltage. Average line voltage compensation is provided
in the gain modulator to ensure constant loop gain over a
wide input voltage range. This compensation includes a
special “brown-out” control which reduces output power
below 90V RMS input.
OVP
11
ILIM
1
IA OUT
2
IA–
3
IA+
4
–
+
–
+
+
VREF _–
–
+
+
0.7V –
SLEEP
UNDER
VOLTAGE
LOCKOUT
R
S
Q
VLIMIT
17V
ISINE
5
VRMS
8
OUT
GAIN
MODULATOR
EA OUT
6
EA–
7
–
VREF
+
SOFT START
9
VREF
OSC
VREF ₁₆
GND
18
VCC ₁₅
OUT
14
PGND
13
RT
12
SYNC
10
CT
17
REV. 1.0.2 6/19/01