LM3450MTSLASHNOPB datasheet(19/42 Pages) TI2

19 / 42 page

356 mV

VAC

DIN

OPTO

0-3V

Analog

Input

VCC

VSB

PWM OUT

Rectified AC

RF1

RF2

CF1

CF2

RPB

RSB

RAC2

RAC1

DIM

VAC

500k

Transition

LM3450/50A

ANGLE

DEMOD

SAMPLE / REMAP

DIN

DOUT

DIN

DOUT

FLT2

FLT1

VADJ

VREF

REF

500 Hz

LM3450

www.ti.com

SNVS681D – NOVEMBER 2010 – REVISED MAY 2013

Figure 26. Dimming Decoder Circuit

PHASE DIMMING DECODER

The LM3450/50A uses the rectified AC line voltage to interpret the conduction angle. Figure 26 shows the

LM3450/50A decoder circuit with associated external circuitry. The rectified AC line voltage is scaled via a

resistor divider (RAC1, RAC2) and connected to the VAC pin. VAC is compared to a 356mV reference to generate a

twice line frequency PWM signal with corresponding duty cycle as shown in Figure 27.

Figure 27. Phase Angle Demodulation

For best results, RAC1 and RAC2 are suggested to be sized so that the VAC voltage crosses the 356mV threshold

when the rectified AC line is as follows:

•

120V systems: 25V to 45V

•

230V systems: 40V to 70V

The demodulated duty cycle is sampled and logarithmically remapped to a 300Hz PWM signal improving the

resolution of low dimming levels to the human eye. A minimum duty cycle limits the maximum achievable

contrast ratio to approximately 70:1. The remapped PWM signal is buffered and output at FLT1 with amplitude

equal to VADJ as shown in Figure 28.

Submit Documentation Feedback

Product Folder Links: LM3450

LM3450MT/NOPB bảng dữ liệu(PDF) 19 Page - Texas Instruments

LM3450MT/NOPB bảng dữ liệu(HTML) 19 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

bảng dữ liệu tải về

Link URL