# Which resistor for my LEDs parallel

I have a LCD Display with white LED backlight. I want to connect it to a MOSFET which will be controlled by my ESP-12E Microcontroller.

I'm wondering which resistor to use. The data sheet says:

Absolute Maximum Ratings: Back Light Forward Current ILED -- 25 mA For each LED

Electrical Characteristics: Forward Current IF -- 20 -- mA Forward Voltage VF -- 3.2 -- V

(4 LEDs parallel)

Question 1:

Is the value per LED?

My power supply will either be 5V or 12V

The other data sheet page says:

LED Backlight Power Supply: max. 3.2V (by 3.3V Power Supply 2-5 Ohm Resistance, or by 5V 20-25 Ohm Resistance)

But if I calculate for 5V power supply I get:

25 Ohms * 0.02 Amps = 0.5 V

Question 2: So does that mean a voltage drop of the resistor of only 0.5 which would result in a voltage of 4.5 V for the LED which seems to be too much?

Or do I have to calculate with 0.08 Amps because of the 4 LEDs?

25 Ohms * 0.08 Amps = 2 V

Question 3:

Would this mean the overall voltage drop is 2 V but every LED still gets 4.5 V?

For 12 V that would mean a 150 Ohms resistor?

I'm not that good at physics, I just want to make sure everything is correct so I don't damage anything.

• This question needs a big tidy-up on formatting. It is too difficult to read. Please also provide a link to the display datasheet. Commented Nov 12, 2017 at 14:45
• Can you share the datasheet of the LCD? Also what is the purpose of using mosfet? Commented Nov 12, 2017 at 15:26
• There are two documents: ecksteinimg.de/Datasheet/CP11005.zip Interface Definition.pdf LCD Panel\TM028HDH01.pdf Commented Nov 12, 2017 at 15:59
• I need the MOSFET because I don't think that the ESP12 can handle that much current. I also want to dim multiple LEDs (15 pieces) along with the LCD backlight at the same time. Commented Nov 12, 2017 at 16:03
• Draw a schematic. Commented Nov 12, 2017 at 16:45