# resolving LM3914

Discussion in 'The Projects Forum' started by ramcaress, Mar 3, 2010.

1. ### ramcaress Thread Starter New Member

Mar 1, 2010
6
0
just want to know how to create a circuit for LM3914 within a range of 4.7V to 5.9V, the 10 LEDs should illuminate when the input voltage is at 5.9V and no LEDs will illuminate at 4.7V input, i had already read the data sheet of LM3914 from national instrument but can't have any idea how to construct, thanks,

Apr 2, 2009
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3. ### SgtWookie Expert

Jul 17, 2007
22,183
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On the link Rifaa posted, look at the Typical Application circuit on page 2.

For the resistor values,
R1: 1,270 Ohms
R2: 4,370 Ohms
You will also need another resistor between pin 4 and ground; a value of 39,167 Ohms.

These values are approximate, and based on the difference between pins 7 and 8 being 1.25v, and the internal resistive divider measuring exactly 10k Ohms.

[eta]
You can't buy resistors with those exact values, but you can use resistors in series and/or parallel to get very close.
Here is a handy online calculator for series/parallel resistance:
http://www.qsl.net/in3otd/parallr.html
Bookmark that page.
For example, if you select E24 values (commonly available) and ask for 1270 Ohms, you'll get output like:
910 + 360 = 1270 (0 %) (This means a 910 Ohm and a 360 Ohm resistor in series to get 1270 Ohms, 0% error)
1600 || 6200 = 1271.795 (0.141 %) (This means a 1.6k and 6.2k resistors in parallel for 1271.795 Ohms; 0.141% error)

You will need to use a supply of at least 8v.

Last edited: Mar 3, 2010
4. ### R!f@@ AAC Fanatic!

Apr 2, 2009
8,793
771
I still wonder why odd values are used in data sheets

5. ### ramcaress Thread Starter New Member

Mar 1, 2010
6
0
got it, its the external resistor combination must be set for the Ref low (4) and Ref high, im goin to reconstruct my old circuit, thanks a lot,