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7 Segment + DP Common Anode Display Driver IC

Discussion in 'General Electronics Discussion' started by [email protected], Dec 17, 2016.

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  1. cRash@101

    [email protected]

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    Dec 17, 2016
    I am looking for a common anode display driver IC. I want to be able to control atleast 6-8 7 segment displays using a single IC. The 7 segment display I have is a 12V common anode. Plz suggest me some common anode diplay driver ICs, i just keep on finding common cathode ones .
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
  3. TedA

    TedA

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    Sep 26, 2011
    To provide help more specific to your requirements, we need to know more about those requirements.

    It would be nice to know the exact display device you have. A link to its datasheet would be ideal, but we need at least the manufacturer and part number.

    How do you plan to generate the signal going to the display driver IC? What sort of signals will you have?

    How do you expect to connect the displays and the driver IC(s)? Will the displays be multiplexed? Or do you intend to have a separate driver pin for each segment of each digit?

    What power supply voltages will be used in your system?

    Signal voltages?

    I'm sure I've missed some parameter that matters; perhaps you will think of it yourself.

    It might also help to know something about your overall intent. Do you need to make one system and get that working, or to prepare a design for production? Is this a hardware project, or is it entirely in the virtual world of simulation?

    I should mention that 12V is not the most usual drive parameter for 7 segment displays, and that if I'm not mistaken, segment driver ICs are actually far more plentiful for common anode displays than for common cathode displays. I expect this harks back to the days when IC design tended to attempt to use only NPN transistors. So it will be interesting to see what sort of display you have.

    Ted
     
  4. sundy

    sundy

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    Aug 5, 2016
    The drive voltage varies from display to display. Our clock displays in 0.56" uses 5 VDC, our 4" uses 12 VDC and our 5" uses 24 VDC. All our displays are common cathode, much easier to control.
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    I beg to disagree. A simple circuit made from an NPN transistor and a resistor allows driving loads with common anode. See our ressource 'using a bipolar transistor to turn a load on and off'. A logic high level voltage - this would be the equivalent of the driving signal for common cathode displays - driving the base via a series resistor turns the transistor on. The LED and current limiting resistor are the load attached to the collector of the transistor.

    This circuit is charming in that it uses e.g. a 3.3 V or 5 V logic level signal to control the transistor, but can easily accomodate much higher voltages (e.g. the 12 V or 24 V you mentioned) on the load side. The transistor decouples this high voltage from the low voltage driving circuit.
     
    davenn likes this.
  6. sundy

    sundy

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    Aug 5, 2016
    I will defer to your assertion. In our industry, wall clocks with at least 4 digits, we use common cathode, we also use display drivers or shift registers that operate on a bus. If I remember correctly the conversation, with an engineer, correctly the common cathode requires less of the current limiting resistors. Not fewer but less demanding specs.
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

    10,806
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    Nov 17, 2011
    I can't imagine why that would be so:
    You need one resistor per segment, regardless of how the segment is driven (common anode vs. common cathode).
    The resistor's parameters (resistance and power dissipation) are also the same as R=V/I and P=I²*R where
    I is given by the LED current (again: independent of the type of connection) and
    V=voltage drop across the resistor=Vcc-Vled (again: independent of the type of connection)
     
    davenn likes this.
  8. sundy

    sundy

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    Aug 5, 2016
    I did it again, for some reason I can't keep common anode and common cathode right in my pea brain. Common anode is the display our industry uses.
     
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