Seiko Instruments G1216B1N000-3D0E =Input voltage power voltageV, =LED forward voltage, Leda Ledc

AN.No.G1216B1N000-3D0E

Limit resistance “R” is calculated using the following equation. The resistance becomes the value shown in Figure 11.

	VIN − VF		VIN	=Input voltage (power voltage)(V)
R=		(Ω)	VF	=LED forward voltage (V)
	IF
			IF	=Allowable LED forward current (A)

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%.

1.2

1.0

0.8

Relative

brightness 0.6 0.5 0.4

0.2

Forward current:

3040 50 60 70 80 90 100 110 IF(mA) Figure 12 Forward Current-Brightness Characteristics (Ta=25°C)

(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.

VIN

R2

R3

R4

LEDA

LEDC

G1216

Tr

Thermistor

R1

Figure 13 LED Backlight Driver Example 2

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