Datasheet

delay
V
BUCK
V
AC
V
BR1
t
?
(a)
(b)
(c)
t
t
V
AC
V
BR1
t
(a)
(b)
(c)
V
BUCK
LM3445
SNVS570L –JANUARY 2009–REVISED MAY 2013 www.ti.com
SENSING THE RECTIFIED TRIAC WAVEFORM
A bridge rectifier, BR1, converts the line (mains) voltage (Figure 15c) into a series of half-sines as shown in
Figure 15b. Figure 15a shows a typical voltage waveform after diode D3 (valley fill circuit, or V
BUCK
).
Figure 15. Voltage Waveforms After Bridge Rectifier Without Triac Dimming
Figure 16c and Figure 16b show typical triac dimmed voltage waveforms before and after the bridge rectifier.
Figure 16a shows a typical triac dimmed voltage waveform after diode D3 (valley fill circuit, or V
BUCK
).
Figure 16. Voltage Waveforms After Bridge Rectifier With Triac Dimming
LM3445 LINE SENSING CIRCUITRY
An external series pass regulator (R2, D1, and Q1) translates the rectified line voltage to a level where it can be
sensed by the BLDR pin on the LM3445.
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