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参数资料
| 型号： | R1218K072A-TR |
| 厂商： | RICOH COMPANY LTD |
| 元件分类： | 稳压器 |
| 英文描述： | 1 A SWITCHING REGULATOR, 1400 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封装： | 1.80 X 2 MM, HALOGEN FREE AND ROHS COMPLIANT, DFN-6 |
| 文件页数： | 18/19页 |
| 文件大小： | 276K |
| 代理商： | R1218K072A-TR |
R1218x
8
(2) Dimming control by DC voltage
LED dimming control is also possible by using the DC voltage to VFB pin. LED current is adjustable by DC
voltage and resistors, R1 and R2 in the following figure.
ILED
=(DC 0.2) / R2 0.2 / R1
DC
VFB
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.
LED current is adjustable according to the "H" level (VH) and "L" level(VL) of PWM signal and resistors,
R1, R2, R3, and R4 in the following figure.
VH
VFB
R3
R2
R1
R4
C3
VL
Dimming controle by filtered PWM signal
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.
ILEDMIN
={0.2 R2 × (VH 0.2) / (R3 + R4)} / R1
ILEDMAX
={0.2 R2 × (VL 0.2) / (R3 + R4)} / R1
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
=10Ω, R2=5.1kΩ,
R3
=51kΩ, 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.
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