7 segment drive

Discussion in 'The Projects Forum' started by hadeedunhaad, Jun 3, 2011.

  1. hadeedunhaad

    Thread Starter New Member

    Apr 22, 2011
    hi all,
    let me first explain what im trying to do so that it would be easy for those trying to help. I'm trying to display more that 50 7-segment leds using a micro contr. All these leds will draw around 0.9 A of current together in worst case. Hence i was trying to drive these leds straight from 12v without passing it through the 5V reg, so that the regulator IC wont get heated up, which is a wastage of energy and will cause unstability in the design. Now since the problem is that our MC works in 5V there has to be something in between to convert the 5v signal (from the MC) to 12v for the shift register IC controlling the 7-segments. I found the following ckt (attached pdf) from this forum and that was a prefect solution. But when everything was set i found out that it doesn't work* and unable to understand why i used my DSO to view the signals. yes , got the problem , the boosting circuit implemented from the pdf is not switching as fast as the signal coming from mc.

    Does any one have a solution for this ? Either i need a boosting circuit which could switch at 8 micro second or a complete alternative for this led driving issue.

    btb i've used the mosfet switching from the pdf.

    Thank you all for your patience and support.

    * i know the circuit and program works well as i'm checking keeping everything in 5 volts.
    • 12V.PDF
      File size:
      7 KB
  2. hadeedunhaad

    Thread Starter New Member

    Apr 22, 2011
    This post has been moved to where ? I thought this was the most suitable section in the forum to post this question.
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    This sounded like a project, so it got moved here. No insult intended.
  4. SgtWookie


    Jul 17, 2007
    Why don't you slow down the microcontroller code, instead of trying to switch at an 8uS rate?
  5. hadeedunhaad

    Thread Starter New Member

    Apr 22, 2011
    Ok, i got the output.

    I did it using darlington pair (ULN2003) and reversed the logic in the program.
    That is i made logic 1 as 0 and logic 0 as 1.
    Connected the outputs of ULN to Vcc through resistors.

    Thank you all guys