LM3914 circuit

Discussion in 'General Electronics Chat' started by Karan_Kapoor, Nov 26, 2014.

  1. Karan_Kapoor

    Thread Starter New Member

    Nov 26, 2014
    6
    0
    Hello

    I want to build a bar graph LED mode with Lm3914N.

    How do I regulate the current for the LED to 30mA?
     
  2. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    hi,
    Iled = 12.5/R1 where R1 is across pins 7 and 8. approx 430R nearest preferred value.
    Do you have more details or circuit diagram.?
    E
     
  3. Karan_Kapoor

    Thread Starter New Member

    Nov 26, 2014
    6
    0
    As you can see in my circuit I took the resistance with 416Ohm, but you can see the Iled is just 10mA.

    Karan
     
  4. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    hi,
    Sorry, the circuit so small I cannot read it.
    E
     
  5. Karan_Kapoor

    Thread Starter New Member

    Nov 26, 2014
    6
    0
    Oh maybe you just click on the pic, it should zoom in.
    Anyway i'm sending you another pic, hope you can read it now
     
  6. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    hi,
    I make close to 30mA on my simulator, how are you measuring the current.?
    I would recommend that you use a max current of 25mA
    E
     
  7. Karan_Kapoor

    Thread Starter New Member

    Nov 26, 2014
    6
    0
    hey
    I don't know which program you use, but I am using circuit wizard and if you start the simulation with this circuit you can move the cursor to the wire and you see the current which is 10mA.
    Karan
     
  8. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    Hi Karan,
    The datasheet for the LM3914 states 12.5/R1, which in my calculation gives approx 30mA and my LM3914 also shows ~30mA, which it should be.

    I see you have a voltage source of 0.7V a 2KHz into Vsig, try a DC voltage without modulation and recheck the current
     
  9. Karan_Kapoor

    Thread Starter New Member

    Nov 26, 2014
    6
    0
    yap according to the calculation 12.5/R1 --> R1~615Ohm the current should be 30mA.

    I think the source of the audio-output of a laptop or a smartpone would be around 0.7V/1kHZ sine or something like that i am not sure.

    Although I use 5V DC, the current remains 10mA. I am just confused and trying to solve the problems for weeks.

    Karan
     
  10. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    hi Karen,
    It could be a problem with your simulator.?
    I would suggest you build the project on a bread board and measure the 'real' LED current.
    Take care not to exceed the total dissipation of the LM3914, which is approx 1Watt, if the LED current is ~30mA and Vsupply of 9V.

    E
    EDIT:
    Try this LM3914 sim.
    http://www.electro-tech-online.com/tools/LM3914V2.php
    This image shows your values in the sim [its Imax of 25mA], in Bar Mode you will require a 15R 1Watt resistor in series with the LED supply.

    Added:
    If you are using a 9V battery say a PP3 type and all 10 LED's are trying to draw 30mA each, in Bar Mode, thats 300mA, which may result in the nominal 9V battery voltage dropping well below 9V, so its possible that you will not be able to maintain 30mA per LED.?
     
    Last edited: Nov 27, 2014
  11. Karan_Kapoor

    Thread Starter New Member

    Nov 26, 2014
    6
    0
    Hi
    I will try this and thanks for your suggestion and help :)

    Karan
     
  12. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    @ericgibbs
    Click not on the image. Click on the words, "circuit.png". New tab opens and THAT image will zoom.
     
  13. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    hi 12,
    Many thanks...;)
    E
     
Loading...