ICL8001G / ICLS8082G
Design Guidelines
Design Optimizations
Application Note
19
Version 2.0, 2011-04-14
5.1.4
Dimmer Selection
With ICL8001G / ICLS8082G control the LED driver can be operated without a wall dimmer as well as using
trailing- and leading-edge dimmers. With the phase-cut dimmers applied above, a satisfying light quality and
variation in the LED lumen flux over the dimming range has been achieved. For both technologies the phase-cut
range should be sufficiently large to provide the dimming range required. The dimming range available with a
particular dimmer for incandescent lamps is directly transferred to the LED driver with ICL8001G / ICLS8082G,
but the lumen output of the LEDs at the minimum dimming position will be higher than with incandescent lamps
as they need a high amount of thermal power to enable the visible light radiation process. Particularly for operation
with 230 V input voltage, leading-edge wall dimmers with a lower rated power range – and hence lower hold-up
current requirements – should be selected in order to prevent the occurrence of repetitive TRIAC ignition.
Operation with lower input voltages, such as 110 V, provides a higher input current, which in principle supports
more stable TRIAC operation.
Touch dimmers with internal IC control, which depends exclusively on a resistive load for sufficient digital IC
supply, should not be selected for LED driver control.
5.2
Power Stabilization for Line Voltage Variations
For stable lumen output and limitation of LED power during mains voltage variations it may be useful to consider
power stabilization for the LED driver design. This can be achieved by appropriate use of IC foldback correction
without additional external components.
5.2.1
Stabilization using IC Foldback Correction
Driver design can be dimensioned in such a way that PLED variation becomes smaller in the range Vin,min < Vin
< Vin,max than would be expected from the approximate quadratic power law. The effect of the foldback correction
on LED power and LED current variations can be enhanced by means of an increased R17 value with a constant
R19. This will modify the input current waveform from sinusoidal to a more rectangular curve. The LED power can
be readjusted by means of the shunt resistor R4. The effect of the foldback correction on the LED power and on
LED current variation can be further increased by additionally lowering the Vcs limit. For this second step the R6
value is decreased.
PLED is readjusted using the shunt resistor R4. The R6 value can be decreased until the latch-off threshold of the
output overvoltage detection is reached. The principal experimental LED current increase for a 10 % input voltage
increase is shown in the following diagram. For input voltage drops, similar behavior is obtained for the LED
current decrease.
