LT1248
Power Factor Controller
U
GND
1
–
+
FEATURES
s
s
s
s
s
s
s
s
s
DESCRIPTIO
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
Fast 1.5A Peak Current Gate Driver
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.
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.
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.
APPLICATIO S
s
s
Universal Power Factor Corrected Power Supplies
Preregulators Up To 1500W
BLOCK DIAGRA
V
CC
16V TO 10V
EN/SYNC
10
V
SENSE
11
I
AC
6
OVP
8
7.9V
7.5V
2.6V/
2.2V
+
–
–
+
–
EA
+
+
–
–
SS
13
12µA
5V
+
ONE SHOT
200ns
–
+
W
U
VA
OUT
7
V
REF
9
7.5V
V
REF
RUN
M
OUT
I
SENSE
5
4
CA
OUT
PK
LIM
3
2
V
CC
15
2.2V
7µA
+
M1
–
I
A
I
2
I
I
M
=
A B
2
32k
I
B
200µA
I
M
–
CA
+
–
+
R
R
RUN
S
Q
16
GTDR
0.7V
SYNC
OSC
1 6V
14
C
SET
12
R
SET
1248 BD
1
LINER [ LINEAR TECHNOLOGY ]
