NSIC2030BT3G Datasheet, PDF (7/9 Pages) ON Semiconductor – Constant Current Regulator & LED Driver for A/C off-line Applications

NSIC2030BT3G
Higher Current LED Strings
Two or more fixed current CCRs can be connected in
parallel. The current through them is additive (Figure 11).
Dimming using PWM
The dimming of an LED string can be easily achieved by
placing a BJT in series with the CCR (Figure 13).
Figure 11.
Other Currents
The adjustable CCR can be placed in parallel with any
other CCR to obtain a desired current. The adjustable CCR
provides the ability to adjust the current as LED efficiency
increases to obtain the same light output (Figure 12).
Figure 13.
The method of pulsing the current through the LEDs is
known as Pulse Width Modulation (PWM) and has become
the preferred method of changing the light level. LEDs being
a silicon device, turn on and off rapidly in response to the
current through them being turned on and off. The switching
time is in the order of 100 nanoseconds, this equates to a
maximum frequency of 10 Mhz, and applications will
typically operate from a 100 Hz to 100 kHz. Below 100 Hz
the human eye will detect a flicker from the light emitted
from the LEDs. Between 500 Hz and 20 kHz the circuit may
generate audible sound. Dimming is achieved by turning the
LEDs on and off for a portion of a single cycle. This on/off
cycle is called the Duty cycle (D) and is expressed by the
amount of time the LEDs are on (Ton) divided by the total
time of an on/off cycle (Ts) (Figure 14).
Figure 12.
Figure 14.
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