April 1998
ML4812*
Power Factor Controller
GENERAL DESCRIPTION
The ML4812 is designed to optimally facilitate a peak
current control boost type power factor correction system.
Special care has been taken in the design of the ML4812
to increase system noise immunity. The circuit includes a
precision reference, gain modulator, error amplifier, over-
voltage protection, ramp compensation, as well as a high
current output. In addition, start-up is simplified by an
under-voltage lockout circuit with 6V hysteresis.
In a typical application, the ML4812 functions as a
current mode regulator. The current which is necessary to
terminate the cycle is a product of the sinusoidal line
voltage times the output of the error amplifier which is
regulating the output DC voltage. Ramp compensation is
programmable with an external resistor, to provide stable
operation when the duty cycle exceeds 50%.
FEATURES
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Precision buffered 5V reference (±0.5%)
Current-input gain modulator reduces external
components and improves noise immunity
Programmable ramp compensation circuit
1A peak current totem-pole output drive
Overvoltage comparator helps prevent output
voltage “runaway”
Wide common mode range in current sense
comparators for better noise immunity
Large oscillator amplitude for better noise immunity
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s
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* Some Packages Are End Of Life
BLOCK DIAGRAM
(Pin Configuration Shown is for DIP Version)
OVP
5
+
SHDN
S
+
–
–
5V
1
–
Q
Q
10
ISENSE
5V
VCC
OUT
12
R
2
3
GM OUT
EA OUT
ERROR
AMP
UNDER
VOLTAGE
LOCKOUT
IEA
PWR GND
11
VREF
VCC
4
EA–
5V
14
13
+
–
32V
6
ISINE
GAIN MODULATOR
GND
15
7
16
RAMP COMP
CT
5V
CLOCK
9
8
RT
OSC
1kΩ
1