LT1249_15 Datasheet, PDF (1/12 Pages) Linear Technology – Power Factor Controller

LT1249
Power Factor Controller
FEATURES
s _{Standard 8-Pin Packages}
s _{High Power Factor Over Wide Load Range}
with Line Current Averaging
s _{International Operation Without Switches}
s _{Instantaneous Overvoltage Protection}
s _{Minimal Line Current Dead Zone}
s _{Typical 250µA Start-Up Supply Current}
s _{Rejects Line Switching Noise}
s _{Synchronization Capability}
s _{Low Quiescent Current: 9mA}
s _{Fast 1.5A Peak Current Gate Driver}
U
APPLICATIO S
s _{Universal Power Factor Corrected Power Supplies}
s _{Preregulators up to 1500W}
, LTC and LT are registered trademarks of Linear Technology Corporation.
DESCRIPTIO
The 8-pin LT^®1249 provides active power factor correc-
tion for universal offline power systems with very few
external parts. By using fixed high frequency PWM current
averaging without the need for slope compensation, the
LT1249 achieves far lower line current distortion, with a
smaller magnetic element than systems that use either peak
current detection or zero current switching approach, in
both continuous and discontinuous modes of operation.
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.
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.
BLOCK DIAGRA
V_SENSE ^7.5V
+
EA
6
–
I_AC
4
VA_OUT
5
I_A
I_B ^32k
1V
M_OUT
CA_OUT
GND
3
2
1
R_MOUT
4k
V_CC +
MULTIPLIER I_M
I_M
=
I_A² I_B
200µA²
15µA
250µA MAX _{16V/10V –}
+
CA
–
g_m = 1/3k
–
+
+
R
S
RUN
+
0.7V
M1
–
+
SYNC ^OSC
7.5V
V_REF
RUN
Q
44µA
22µA
4k
–
20µA
16V
35pF
V_CC
7
GTDR
8
1249 BD
1