April 1998
ML4812*
Power Factor Controller
GENERAL DESCRIPTION
FEATURES
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, overvoltage 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.
s
Precision buffered 5V reference (±0.5%)
s
Current-input gain modulator reduces external
components and improves noise immunity
s
Programmable ramp compensation circuit
s
1A peak current totem-pole output drive
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%.
s
Overvoltage comparator helps prevent output
voltage “runaway”
s
Wide common mode range in current sense
comparators for better noise immunity
s
Large oscillator amplitude for better noise immunity
* Some Packages Are End Of Life
BLOCK DIAGRAM
(Pin Configuration Shown is for DIP Version)
OVP
ISENSE
3
4
10
Q
R
+
–
–
5V
2
S
–
5V
1
SHDN
+
5
Q
VCC
OUT
12
PWR GND
GM OUT
11
EA OUT
EA–
+
5V
UNDER
VOLTAGE
LOCKOUT
ERROR
AMP
ISINE
VCC
–
IEA
6
VREF
14
13
32V
GAIN MODULATOR
GND
15
7
16
5V
RAMP COMP
CT
CLOCK
9
8
RT
OSC
1kΩ
1
