SM8121A

NIPPON PRECISION CIRCUITS INC.—13

Current Switching using External Transistors

If only a few brightness steps are required, the LED current can be adjusted by switching the LED current set-

ting resistance using external transistors (Tr).

SW

VSS

FB

SM8121

R1

250

Ω

SBD

Select signal 1

Tr1

R2

100

Ω

VDD

CE

1.0

µF

L

10

µH

4.7

µF

3.6V

LED

Select signal 2

Tr2

R3

40

Ω

Select signal 2

Select signal 1

Low

Low

2mA

Low

High

2 + 5 = 7mA

High

Low

2 + 12.5 = 14.5mA

High

High

2 + 5 + 12.5 = 19.5mA