LT1249
Power Factor Controller
U
FEATURES
DESCRIPTIO
The 8-pin LT®1249 provides active power factor correc-
tion for universal offline power systems with very few
externalparts.ByusingfixedhighfrequencyPWMcurrent
averaging without the need for slope compensation, the
LT1249 achieves far lower line current distortion, with a
smallermagneticelementthansystemsthatuseeitherpeak
current detection or zero current switching approach, in
both continuous and discontinuous modes of operation.
■
Standard 8-Pin Packages
■
High Power Factor Over Wide Load Range
with Line Current Averaging
■
International Operation Without Switches
■
Instantaneous Overvoltage Protection
■
Minimal Line Current Dead Zone
■
Typical 250µA Start-Up Supply Current
■
Rejects Line Switching Noise
■
Synchronization Capability
The LT1249 uses a multiplier containing a square gain
function from the voltage amplifier to reduce the AC gain
at light output load and thus maintains low line current
distortion and high system stability. The LT1249 also
provides filtering capability to reject line switching noise
which can cause instability when fed into the multiplier.
Line current dead zone is minimized with low bias voltage
at the current input to the multiplier.
■
Low Quiescent Current: 9mA
■
Fast 1.5A Peak Current Gate Driver
U
APPLICATIO S
■
Universal Power Factor Corrected Power Supplies
Preregulators up to 1500W
■
The LT1249 provides many protection features including
peak current limiting and overvoltage protection. The
switching frequency is internally set at 100kHz.
While the LT1249 simplifies PFC design with minimal
parts count, the LT1248 provides flexibilities in switching
frequency, overvoltage and current limit.
, LTC and LT are registered trademarks of Linear Technology Corporation.
W
BLOCK DIAGRA
CA
M
GND
1
V
VA
OUT
OUT
3
CC
7
OUT
2
5
7.5V
REF
V
R
4k
MOUT
+
–
7.5V
V
SENSE
6
+
–
V
RUN
EA
CC
I
I
A
250µA MAX
16V/10V
MULTIPLIER
2 I
I
M
I
AC
32k
1V
+
I
A
B
I
=
B
M
4
200µA2
–
+
CA
–
R
S
Q
GTDR
8
15µA
+
g
= 1/3k
RUN
m
+
0.7V
M1
–
OSC
+
–
SYNC
4k
16V
44µA
22µA
20µA
35pF
1249 BD
1