April 1997
ML4813*
Flyback Power Factor Controller
GENERAL DESCRIPTION
The ML4813 is a PWM controller designed for use in a
discontinuous "flyback" or "buck-boost" type power factor
correction (PFC) system for low power, low cost
applications.
The circuit includes a precision reference, oscillator, error
amplifier, over-voltage comparator, over-current
comparator, and an extra op-amp as well as a high
current output. In addition, start-up is simplified by an
under-voltage lockout circuit.
In a typical application, the ML4813 functions as a
voltage mode regulator. By maintaining a constant duty
cycle, the current follows the input voltage, making the
impedance of the entire circuit appear purely resistive.
With the flyback circuit, power factors of 0.99 are easily
achievable with a small output inductor and a minimum
of external components.
FEATURES
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Precision buffered 5V reference
Extra op-amp for output voltage instrumentation
amplifier
Overcurrent comparator for switch protection
Soft start and under-voltage lockout for easy low surge
off-line starting
1A peak current Totem-pole output drive
Overvoltage comparator eliminates output "runaway"
due to load removal
Large oscillator amplitude for better noise immunity
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* This Part Is End Of Life As Of August 1, 2000
BLOCK DIAGRAM
VFB
4
-
ERROR
AMPLIFIER
OA OUT
7V
OA+
+
8
7
6
5V
+
60µA
SOFT START
2
-
OA-
VREF
14
ILIMIT
1
+
CURRENT LIMIT
COMPARATOR
UNDERVOLTAGE
LOCKOUT
VCC
13
1V
OVP
5
-
32V
OVP
COMPARATOR
S
Q
Q
+
OUT
12
5.6V
COMP
3
-
R
-
+
PWR GND
11
CT
16
PWM
COMPARATOR
GND
RT
9
OSCILLATOR
SYNC
15
10
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
