R1218x

7

(2) Dimming control by DC voltage

voltage and resisters, R1 and R2 in the following figure.

=(DC − 0.2) / R2 − 0.2 / R1

DC

R1

R2

Dimming control by DC voltage

(3) Dimming control by feedback voltage and filtered PWM signal

LED dimming control is also possible by using the feedback voltage and filtered PWM signal.

R3

R2

R1

R4

C3

Dimming controle by filtered PWM signal

R1, R2, R3, and R4 in the figure5. Duty

=0% to 100% PWM signal duty cycle can be used up to the

maximum LED current and minimum LED current as in the next formulas.

For example, supposed that the PWM signal level is set as 2.5V/0V, to adjust the LED current range from 0mA

to 20mA by the duty cycle, our recommendation external components values are, R1=10

Ω, R2=5.1kΩ,

R3=51k

Ω, R4=5.1kΩ or around.

C3 should be set large enough to regard the PWM signal as adjustable DC voltage by the filter. In this method,

higher frequency control than the frequency against the CE pin can be used for dimming control.

For example, if the frequency is 40kHz, 0.1

µF or more capacitor is our recommendation value as C3.