SNVS570L – JANUARY 2009 – REVISED MAY 2013
SIMPLIFIED INTERNAL BLOCK DIAGRAM
VCC
BLDR
ANGLE DETECT
INTERNAL
REGULATORS
LM3445
7.2V
230
BLEEDER
4 P s
V CC UVLO
THERMAL
MOSFET
COFF
COFF
SHUTDOWN
DRIVER
GATE
33 :
1.276V
START
S
Q
ASNS
0V to 4V
DIM DECODER
750 mV
50k
R
LATCH
FLTR1
4.9V
Tri-State
RAMP
370k
PWM
CONTROLLER
I-LIM
DIM
RAMP GEN.
5.9 kHz
3V
1V
1.27V
1k
ISNS
LEADING EDGE BLANKING
FLTR2
125 ns
GND
Figure 11. Simplified Block Diagram
APPLICATION INFORMATION
FUNCTIONAL DESCRIPTION
The LM3445 contains all the necessary circuitry to build a line-powered (mains powered) constant current LED
driver whose output current can be controlled with a conventional triac dimmer.
OVERVIEW OF PHASE CONTROL DIMMING
A basic "phase controlled" triac dimmer circuit is shown in Figure 12 .
BRIGHT
R1
250 k ?
DIM
TRIAC
MAINS AC
R2
C1
3.3 k ?
DIAC
100 nF
LOAD
Figure 12. Basic Triac Dimmer
Copyright ? 2009–2013, Texas Instruments Incorporated
Product Folder Links: LM3445
7
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