Seiko Instruments G1216B1N000-3D0E

AN.No.G1216B1N000-3D0E

- 22 -

Limit resistance “R” is calculated using the following equation. The resistance becomes the value

shown in Figure 11.

R= VIN

−

VIN =Input voltage (power voltage)(V)

VF=LED forward voltage (V)

IF=Allowable LED forward current (A)

(

Ω

)

For this resistance value, the forward current becomes lower than 50 mA at 25°C. The surface

brightness of the LED backlight varies with the forward current. See Figure 12. Compared with 1.8 (4)

brightness (IF=90 mA), the brightness is about 40%.

Forward current:

IF(mA)

0.2

0.4

0.6

0.8

1.0

30 40 50 60 70 80 90 100 110

Relative

brightness 0.5

1.2

(2) Example 2

When you want to keep the brightness (2 nit) at 25°C, use a thermosensitive element, like a thermistor,

and a transistor as shown in Figure 13. Set the thermosensitive element to about IF=90 mA at 25°C

and configure it so that “IF” will be reduced as the temperature rises.

G1216

VIN

LEDA

LEDC

Thermistor

Figure 12 Forward Current-Brightness Characteristics (Ta=25°C)

Figure 13 LED Backlight Driver Example 2