LM3450AEV230V30/NOPB National Semiconductor, LM3450AEV230V30/NOPB Datasheet - Page 17

• Manufacturer Part Number: LM3450AEV230V30/NOPB
• Description: LM3450A EVAL BOARD 230V30
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3450AEV230V30/NOPB

• Current - Output / Channel: 700mA
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 50V
• Features: -
• Voltage - Input: 180 ~ 265VAC
• Utilized Ic / Part: LM3450A
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

PHASE DIMMING DECODER
The LM3450 uses the rectified AC line voltage to interpret the
conduction angle.
cuit with associated external circuitry. The rectified AC line
voltage is scaled via a resistor divider (R
nected to the V
to generate a twice line frequency PWM signal with corre-
sponding duty cycle as shown in
For best results, R
that the V
rectified AC line is as follows:
•
•
The demodulated duty cycle is sampled and logarithmically
remapped to a 300Hz PWM signal improving the resolution
120V systems: 20V to 30V
230V systems: 40V to 60V
FIGURE 11. Phase Angle Demodulation
AC
voltage crosses the 356mV threshold when the
AC
pin. V
AC1
Figure 10
and R
AC
is compared to a 356mV reference
AC2
shows the LM3450 decoder cir-
are suggested to be sized so
Figure
11.
AC1
, R
FIGURE 10. Dimming Decoder Circuit
AC2
30127432
) and con-
17
of low dimming levels to the human eye. A minimum duty cy-
cle limits the maximum achievable contrast ratio to approxi-
mately 70:1. The remapped PWM signal is buffered and
output at FLT1 with amplitude equal to V
ure
The FLT1 signal is routed through a 2 pole low pass filter
(R
twice line frequency ripple. The resulting analog signal at
FLT2 is compared to a 500Hz Triangle wave to create the
inverted PWM signal at the DIM pin as shown in
F1
12.
, C
F1
, R
FIGURE 12. FLT1 to FLT2 Mapping
FIGURE 13. FLT2 to DIM Mapping
F2
, C
F2
), as shown in
30127431
Figure
ADJ
10, to remove the
as shown in
www.national.com
30127434
30127433
Figure
13:
Fig-