# LM3914 Help!

Discussion in 'The Projects Forum' started by TehDawg, Aug 18, 2011.

1. ### TehDawg Thread Starter New Member

Feb 4, 2011
8
0
Hi Forum!

I'm currently building a 0-20V power supply using a L200, and would like to make 5 led bar display as a 'look good' feature. Im planning on using a lm3914 driver since I have one laying around.
I looked at the datasheets and simply did not understand how this driver works.
How would I have the driver light up one led every 4V? What is the reference voltage used for? and do I need to be concerned about excessive current draw, since it is a power supply and I dont want to waste too much power on LED's and drivers.

Thank you very much!

Regards

2. ### #12 Expert

Nov 30, 2010
16,705
7,358
Is this a better datasheet than what you have?

Ps, It's always good for you, the original poster, to provide a datasheet. It saves us time and eliminates a basic question like this one that I have posted.

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3. ### praondevou AAC Fanatic!

Jul 9, 2011
2,936
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The adjustable reference voltage is applied to the internal resistor string on the LED comparator inputs. That's the voltage you are comparing the signal input voltage to. If you use the simplest application applying the reference voltage of 1,25V to the resistor string and you want 5 LEDs and every LED to light up every 4V, bring down the signal input voltage (20V) to a bit more than 625mV. You can do this with a voltage divider or an opamp attenuator.
This way the lower 5 LEDs will light up, 1 to 5 for 4V to 20V.

4. ### iONic AAC Fanatic!

Nov 16, 2007
1,422
68
The datasheet also describes a way to use "dot mode" (1 LED lights up an any given time) or "bar mode" (LED's light up consecutively as voltage increases). Also, the datasheet describes how to limit the current to the LED's, I believe to as little as 10mA/LED.