XC9116
Series
■APPLICATION
INFORMATION (Continued)
<Dimming Control (Continued)>
3. Using DC Voltage
If in an application it is necessary to control the LED current by a variable DC voltage, illumination control of LED is
achieved by connecting R1 and R2 and applying a direct-current voltage to R2, as shown below.
When R1>>R
LED
, I
LED
which flows into LEDs can be calculated by the following equation;
I
LED
= (V
REF
- R1 / R2 (V
DC
- V
REF
)) / R
LED
V
REF
= 0.2V (TYP.)
Ex.1) When R1 = 10k
Ω
, R2 = 100k
Ω
, R
LED
= 10
Ω
,
In the range of 0.2V to 2.2V DC, I
LED
(LED current) varies between 20mA to 0mA.
ZD
XC9116
FB
VDC
R2
ILED
(
)
R1
RLED
Figure : Circuit using DC voltage
Ex.2) When R1 = 10k
Ω
, R2 = 100k
Ω
, R3 = 10k
Ω
,
C1 = 0.1µF, RLED = 10Ω, the average LED current will
be 10mA by inputting a PWM signal of CE ‘H’ level:
2.2V, CE ’L’ level: 0V, duty cycle: 50%, oscillation
frequency: 100Hz. As well as the way of dimming
control by applying the PWM signal to the CE pin, the
average LED current increases proportionally with the
positive duty cycle of the PWM signal.
ZD
XC9116
FB
PWM
R3
C1
R2
ILED
(
)
R1
RLED
Figure : Circuit inputting a PWM signal to the FB pin
<Prevent Emission Caused by White LEDs Leakage>
When the input voltage (V
IN
) is high, minimum illumination may occur to the CE pin even in the disable state. If this
happens, please connect a transistor to between the LED and the FB pin. By driving the CE signal in-phase and cutting
the pass to current, the minimum illumination can be prevented.
L:22uH
VLF3010A
VIN
3.6V
(3.2V~6.0V)
SD
XB0ASB03A1B
VIN
CIN
4.7uF
CE
GND
Lx
XP151A21A2
FB
RLED
10Ω
20mA
CL
0.22uF
(base)
8/22
TOREX [ TOREX SEMICONDUCTOR ]
