ICL8001G / ICLS8082G
Design Guidelines
Design Optimizations
Application Note
15
Version 2.0, 2011-04-14
5
Design Optimizations
5.1
Dimming
5.1.1
Dimming Principle
The LED driver input voltage at phase cut dimming with the switching instant ts will generate an effective voltage
of
Vineff(ts)
. From the applied dimming principle it can be seen that the LED power will depend on
Vineff(ts)
according to the proportionality law
(24)
where 1.5 < x < 2.0. Consequently, the light level depends on the RMS input voltage
Vrms(ts)
provided by the
phase cut dimmer and the dimming range is therefore given by the phase-cut limits of the wall dimmer. For the
example of a trailing edge dimmer, the following diagrams show the time dependence of the modified input voltage
V(t,ts)
with the fixed parameter switching instant ts = T/4 and the RMS input voltage
Vrms(ts)
during a theoretical
full variation of switching instants ts for visualization of the mathematical function
Vrms(ts)
.
Figure 7
Timing dependency on input voltage
Figure 8
Timing dependency on RMS input voltage
x
ts
Vrms
ts
Vrms
PLED
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