BRIGHT

DIM

MAINS AC

R1

250 kÖ

DIAC

LOAD

R2

3.3 kÖ

C1

100 nF

TRIAC

LM3445

7.2V

S

R

Q

PWM

I-LIM

1.27V

ISNS

ASNS

COFF

MOSFET

DRIVER

GND

FLTR1

FLTR2

DIM

VCC

ANGLE DETECT

BLEEDER

DIM DECODER

1.276V

4.9V

RAMP

0V to 4V

THERMAL

SHUTDOWN

50k

370k

1k

RAMP GEN.

5.9 kHz

3V

1V

INTERNAL

REGULATORS

750 mV

33:

125 ns

LEADING EDGE BLANKING

Tri-State

COFF

LATCH

CONTROLLER

START

4 Ps

BLDR

230

GATE

LM3445

www.ti.com

SNVS570K – JANUARY 2009 – REVISED NOVEMBER 2011

SIMPLIFIED INTERNAL BLOCK DIAGRAM

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.

Figure 12. Basic Triac Dimmer

Copyright © 2009–2011, Texas Instruments Incorporated

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