LED voltage and current of TFT LCD display backlight

了解TFT LCD显示屏背光的参数（比如3S7P、工作电压、电流、功率）在设计、选型、驱动、可靠性等多个方面都非常重要。常见的7寸TFT LCD显示屏，背光结构为 3串7并（3S7P），我们来逐步计算出背光的电压、电流与功率。

For a 7-inch 1024×600 display screen, if the backlight is configured as 3 series 7 parallel (3S7P), the backlight operating voltage is approximately 9 V, the current is approximately 140 mA, and the power is approximately 1.26 W.

3 series 7 parallel (3S7P):

S = Series
P = Parallel

3-string: Each string contains 3 LEDs connected in series, and the voltages of the series LEDs are added together.

7 parallel: There are 7 such series branches connected in parallel, and the currents of the parallel branches are added together.

Forward voltage	Vf	3.0 V (Typical)	Voltage of white LED at 20 mA
Operating current	If	20 mA (typical)	Recommended current for each LED

Series section (voltage per series)

Each LED has a voltage of approximately 3.0 V, and three LEDs are connected in series:

V = 3 × 3.0 V = 9.0 V

Therefore, the backlight driver needs to provide a constant current output of about 9V (slightly higher than 9V, such as 9.5V–10V to ensure driving margin).

Parallel connection (total current)

Each string of LEDs draws approximately 20 mA, and there are 7 LEDs connected in parallel:

I = 7 × 20 mA = 140 mA

Backlight power calculation

P = V × I = 9 V × 0.14 A = 1.26 W

The total power consumption of the backlight is approximately 1.26 W.

参数	Calculated value	Description
Each voltage	≈ 9 V	3 LEDs in series
Total current	≈ 140 mA	7 parallel
Backlight power	≈ 1.26 W	9 V × 0.14 A
Recommended driver method	Boost constant current LED driver	Output 9~10 V constant current 140 mA
dimming method	PWM or analog current regulation	Commonly used for brightness control

Backlighting is the most power-consuming component of an LCD display (accounting for approximately 80% of the total screen power consumption). Understanding LED voltage and current allows for the calculation of power consumption.

P = V×I

For example: 4S7P

P = V × I = 12 V × 0.14 A = 1.68 W

If a 12V power supply is used with an 85% conversion efficiency, the entire system will consume approximately 1.48W more. This can be used to design the heat dissipation, power consumption budget, and battery capacity.

Current	brightness	LED Lifespan (relative)
10mA	Approximately 50% brightness	Approximately twice the lifespan
20mA	100% brightness	Standard lifespan
25mA	Super Bright	Life expectancy decreases by approximately 30%.

For applications involving TFT LCD displays that require specialized expertise (such as industrial, automotive, high-brightness, and wide-temperature environments), Hongcai Technology has extensive practical experience in designing and customizing backlights to ensure environmental tolerance (temperature, lifespan, brightness decay) and driver compatibility (constant current requirements, PWM dimming support).