SM8120A

NIPPON PRECISION CIRCUITS INC.—8

Brightness adjustment using FB pin (PWM signal input)

tion 4.

If the values R1 = 30

If the values R1 = 30

Taking the above diagram as an example, inserting the values R1 = 30

Ω, R2 = 20kΩ, R3 = 50kΩ, R4 = 50kΩ,

tion 6).

Brightness adjustment circuit using FB pin

(PWM signal input)

SW

VSS

FB

R1

30

Ω

SBD

R3

50k

Ω

R2

20k

Ω

VDD

CE

1.0

µF

L

22

µH

4.7

µF

3.6V

LED

R4

50k

Ω

C1

0.1

µF

PWM signal

Duty [

%]

PWM signal vs. LED current

0

5

10

15

20

0.0

0.5

1.0

1.5

2.0

2.5

3.0

× Duty [V]

R2

R3 +R4

R1

−

... (4)

30

30

=

20,000

× (3 × 0 − 0.5)

50,000 + 50,000

0.5

−

0.6

20mA

... (5)

30

30

=

20,000

× (3 × 1 − 0.5)

50,000 + 50,000

0.5

−

0

0mA

... (6)