DAC and LM324

Discussion in 'General Electronics Chat' started by talhaali, Jun 28, 2012.

  1. talhaali

    Thread Starter New Member

    Nov 24, 2011
    19
    0
    hi , i am trying to connect output of DAC0808 i.e its 4th pin to LM324 ,i want to get output of LM324 to be negative . now when i give positive voltage at Vref(+) i.e pin 14 of DAC of dac i get a positive voltage at output of LM324 ,but when i give negative voltage on this same pin i get zero output of LM324.
    similarly when i give negative voltage at Vref(-) i.e pin 15 i get positive output of LM324 and gving a positive voltage at same pin gives zero output.please help
    in proteus it is runing the proper way i want but i am facing this issue in hardware.proteus file is attatched
     
  2. talhaali

    Thread Starter New Member

    Nov 24, 2011
    19
    0
    its urgent friends please guide me
     
  3. upand_at_them

    Active Member

    May 15, 2010
    246
    29
    Eight minutes and your crying for a reply? Give it some time, man. The people on here are providing help FOR FREE.
     
  4. talhaali

    Thread Starter New Member

    Nov 24, 2011
    19
    0
    ppl here always helped me , n m nt crying i jst asked 4 urgent help cux i hv 2 complete things in a few hours time
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    What voltages are the power supply pins on your DAC and your LM324 connected to?
     
  6. talhaali

    Thread Starter New Member

    Nov 24, 2011
    19
    0
    DAC is given 10v at refrence n DAC power suply pins r coected to 5v n ground n LM324 is connected to +15v n -15v
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,731
    4,789
    If the DAC is powered by 5V and ground, and the output is going to a node that is being held at virtual ground, how is the DAC expected to draw current from that node? Where is that current supposed to go?
     
  8. WBahn

    Moderator

    Mar 31, 2012
    17,731
    4,789
    This isn't Twitter. Please use complete sentences and not cute texting shorthand.

    And posting a follow-up because you haven't received a replay after just 8-minutes is quite unreasonable. Don't be surprised if it sometimes takes a couple of days (or longer) for it to catch the attention of someone that cares enough to respond.
     
  9. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    You can't make the DAC0808 source current, but you can add an offsetting current (through R1), so that the op amp output will swing positive and negative.
    The DAC output sinks 0 to 2mA, controlled by the digital inputs. R1 sources 1mA. The result is that ±1mA flows through R3, for ±10V at the output.
    Note that the output will be at zero when the input code is 80 hex (128 decimal or 10000000 binary).
    Note also that you MUST have a negative supply for Vee on the DAC.
     
Loading...