ML4821IS MICRO-LINEAR [Micro Linear Corporation], ML4821IS Datasheet - Page 7

• Manufacturer Part Number: ML4821IS
• Description: Power Factor Controller
• Manufacturer: MICRO-LINEAR [Micro Linear Corporation]

The output of the gain modulator is a current which
appears on IA+ to form the reference for the current error
amplifier and is given as:
The output current of the gain modulator is limited to:
This sets the system current limit.The multiplier output
current is converted into the reference voltage for the
current (IA) amplifier through a resistor to ground on IA+.
Figure 5. Output Saturation Voltage vs. Output Current.
–1.0
–2.0
where:
Figure 3. Error and Current Amplifier Configuration
3.0
2.0
1.0
S.S
INV
9
0
0
7
I
is the output of the error amplifier and K is a
constant determined by the V
0
SINE
+8V
is the current in the dropping resistor, V
V
CC
I
T
GM
A
200
= 25°C
I
O
, OUTPUT LOAD CURRENT (mA)
K I
I
GM MAX
T
A
V
SOURCE SATURATION
(LOAD TO GROUND)
REF
= –55°C
(
SINE
SINK SATURATION
T
(LOAD TO V
A
–
+
400
)
= –55°C
(
V
. 2 5
R
EA
T
RMS
6.2k
CC
0 8
input.
)
. )
+8V
600
80 s PULSED LOAD
GND
120 Hz RATE
V
CC
T
= 15V
A
EA OUT
EA
= 25°C
6
Micro Linear
800
Figure 6 shows the gain adjustor (K) with respect to the
voltage at V
parts. The right hand part is for operation under normal
conditions in the voltage range from minimum line
voltage to maximum line voltage (90VAC to 260VAC).
85VAC on the curve has been chosen to account for
tolerances. Under normal operating conditions as input
voltage decreases the gain increases compensating for the
drop in the loop gain.
Under brownout conditions (below 85VAC) the gain
decreases to limit the amount of current that is drawn
from the line thus preventing an overload condition. This
is a very useful feature since in many cases the load for a
PFC is a constant power load. The input current has to go
high to compensate for a drop in the input voltage.
Figure 4. Error Amplifier Open-loop Gain and Phase vs.
100
–20
80
60
40
20
K
0
10
0.5
0.4
0.3
0.2
0.1
Figure 6. K-factor. Gain Modulator gain with
0
0
DESIGN
FOR
BROWNOUT
100
RMS
OPERATING BOUNDRY
respect to the voltage at V
1
. The curve has been separated in two
0.23
85VAC
1.0k
GAIN
2
f, FREQUENCY (Hz)
Frequency.
120VAC
DESIGN
FOR
NORMAL
OPERATIONS
10k
3
V
THIS IS THE MINIMUM
OPERATING
VOLTAGE POINT
RMS
4
100k
THIS GAIN CURVE TAKES
OUT THE 1/(V
DEPENDENCY OF THE
VOLTAGE CONTROL LOOP
V
V
R
T
L
A
CC
O
= 25°C
220VAC
= 100k
5
= 1.0V TO 5.0V
= 15V
RMS
1.0M
PHASE
IN
ML4821
)
.
2
6
10M
7
0
–30
60
90
120
150
180
7