LT1248
Power Factor Controller
U
FEATURES
DESCRIPTIO
The LT®1248 provides active power factor correction for
universal off-line power systems. By using fixed high
frequency PWM current averaging, without the need for
slope compensation, the LT1248 achieves far lower line
current distortion with a smaller magnetic element than
systems that use either peak-current detection or zero
current switching approaches in both continuous and
discontinuous modes of operation.
■
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
■
Low Quiescent Current: 9mA
The LT1248 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 LT1248 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.
■
Fast 1.5A Peak Current Gate Driver
U
APPLICATIO S
■
Universal Power Factor Corrected Power Supplies
Preregulators Up To 1500W
■
The LT1248 provides many protection features including
peak current limiting and overvoltage protection, and can
be operated at frequencies as high as 300kHz.
, LTC and LT are registered trademarks of Linear Technology Corporation.
W
BLOCK DIAGRA
CA
M
I
GND
1
V
CC
15
V
PK
LIM
VA
OUT
3
OUT SENSE
REF
9
OUT
4
5
2
7
–
+
7.5V
REF
+
–
V
V
CC
16V TO 10V
RUN
2.6V/
–
+
2.2V
7.5V
EN/SYNC
10
7µA
2.2V
+
M1
–
V
SENSE
11
–
I
I
A
–
+
EA
I
M
I
2 I
B
CA
+
A
I
AC
I
M
=
32k
200µA2
B
R
R
–
+
6
Q
+
–
7.9V
OVP
8
S
+
–
RUN
16
0.7V
SYNC
GTDR
–
+
ONE SHOT
200ns
OSC
12µA
5V
SS
13
1 6V
14
12
1248 BD
C
SET
R
SET
1