How to calculate the current limiting resistor?

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Xtrabuilds
Posts: 6
Joined: Wed Sep 12, 2018 6:19 pm

How to calculate the current limiting resistor?

Post by Xtrabuilds » Tue Oct 30, 2018 10:09 pm

How do you calculate the value of the current limiting resistor?

LCD_Designs
Posts: 262
Joined: Thu Feb 22, 2018 9:49 pm

Re: How to calculate the current limiting resistor?

Post by LCD_Designs » Tue Oct 30, 2018 10:13 pm

It is important to choose the correct value current limiting resistor for the backlight. The wrong value will make the backlight too bright and burn it out or too dim and you won't be able to read the LCD at night. Sometimes it is best to connect a 10K pot so you can adjust to the best brightness and then take a measurement.

Below is the equation to locate the best value:
R (limit) = (Voltage of backlight – 4.2V) / 0.12A

The answer/value will be in ohms

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