ML4813 Datasheet, PDF (1/15 Pages) Micro Linear Corporation – Flyback Power Factor Controller

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
s Precision buffered 5V reference
s Extra op-amp for output voltage instrumentation
amplifier
s Overcurrent comparator for switch protection
s Soft start and under-voltage lockout for easy low surge
off-line starting
s 1A peak current Totem-pole output drive
s Overvoltage comparator eliminates output "runaway"
due to load removal
s Large oscillator amplitude for better noise immunity
* This Part Is End Of Life As Of August 1, 2000
BLOCK DIAGRAM
VFB
4
ERROR
AMPLIFIER
-
5V +
SOFT START
2
ILIMIT
1
1V
CURRENT LIMIT
COMPARATOR
+
-
OVP
5
5.6V
OVP
COMPARATOR
+
-
COMP
3
CT
16
RT
9
SYNC
10
-
+
PWM
COMPARATOR
OSCILLATOR
7V
60µA
UNDERVOLTAGE
LOCKOUT
SQ
RQ
OA OUT
6
OA+
8
7
OA-
VREF
14
VCC
13
32V
OUT
12
PWR GND
11
GND
15
1