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

Micro Linear
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.
BLOCK DIAGRAM
May 1997
ML4821*
Power Factor Controller
FEATURES
s Average current sensing for lowest possible
harmonic distortion
s Average line compensation with brown-out control
s Precision buffered 5V reference
s 1A peak current totem-pole output drive
s Overvoltage comparator eliminates output “runaway”
due to load removal
s Wide common mode range in current sense
comparators for better noise immunity
s Large oscillator amplitude for better noise immunity
s Output driver internally limited to 17V
s “Sleep mode” shutdown input
* Some Packages Are Obsolete
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
V_RMS
8
OUT
GAIN
MODULATOR
EA OUT
6
EA–
7
–
V_REF
+
SOFT START
9
VREF
OSC
Micro Linear
VREF ₁₆
GND
18
VCC ₁₅
OUT
14
PGND
13
R_T
12
SYNC
10
CT
17
1