For LCD, I have to make back-light voltage provision.

As per below image, LEDK1 to LEDK4 pins are internally grounded in LCD module itself.

But I have to add series resistor to limit current.

LED Pins

LED specification in LCD is as follows:


Is it good option to have common resistor to all LED's? What value should I choose if VF=3.2V (typ), IF-25 mA (max) for each LED.


What value of If should I consider to put it in below equation: Rs= Vs-Vf/(If)? Is it for single LED (25mA) or for 4 LED's (100mA)?


Nothing changes. Calculate the resistor as normal (Vin- Vf) / If. The leds were chosen to match each other, and even if they are in parallel with a single resistor it is okay if you pay attention to the specs.

As it says, the remark is the the leds are in parallel, and they still give a 25 mA max current, so that's the maximum you want, not 4 x 25 mA.

  • \$\begingroup\$ Thank you sir..I have attached one more image..pls go through and suggest. \$\endgroup\$ – Electroholic Mar 2 '16 at 10:36
  • \$\begingroup\$ @electroholic the update shows additional notes that indicate I'm wrong, but spher shows that the schematic may already have a resistor for this. Check for R5, a 3.9 ohm resistor. \$\endgroup\$ – Passerby Mar 2 '16 at 10:54
  • \$\begingroup\$ Sorry My bad. I attached wrong link. Updated now. Please check. \$\endgroup\$ – Electroholic Mar 2 '16 at 11:07
  • \$\begingroup\$ @Passerby looks like the "Power Consumption" rating of 256mW confirms that it's 20mA per each parallel LED, 80mA total. With that said, I've just spent 20-30mins digging through Google results & datasheets, but I still can't find anything that states whether of not there's already an internal resistor on these LEDs. \$\endgroup\$ – Robherc KV5ROB Mar 2 '16 at 13:42

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