uln 2003 for driving 7-segment

Discussion in 'General Electronics Chat' started by pii.inc, Jun 15, 2012.

  1. pii.inc

    Thread Starter New Member

    Jun 15, 2012
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    I want to ask how the analysis of darlington circuit in the ULN 2003. i have 7-segment input voltage = 2V, I per segment = 20 mA, how to calculate RU on this circuit?
    thank you

    the circuit:
    http://www.freeimagehosting.net/6ge8y
    [​IMG]
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    For a supply voltage of V:

    R = (V - 2 volts) / 20 mA

    but I'm guessing since I have not seen your circuit.
     
  3. pii.inc

    Thread Starter New Member

    Jun 15, 2012
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    the input of ULN 2003 drived by mikrokontroler,

    I have seen this equation
    Ra-g = (VCC - (Vce_on + Vsevsegment+ VolULN) / Isevsegmet.
    but I don't know the means of Vce_on and Vol ULN

    this is the full circuit.

    http://www.freeimagehosting.net/nu4m1
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Vol is output voltage (low) of the UN2003. In the datasheet, it is Vce(sat). Vce_on is the Vce(sat) of the PNP segment driver.
    Look at it like this: The voltage across the resistor is VCC, minus the voltage across the seven segment device, minus the saturation voltage of the ULN2003, minus the saturation voltage of the segment driver PNP. That's because the PNP, the 7seg, the resistor, and the ULN2003 are all in series.
     
  5. pii.inc

    Thread Starter New Member

    Jun 15, 2012
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    thank you ron,
    i saw from source that equation, Vol ULN2003 = 0,2 V. in datasheet ULN 2003A there are 3 Vce(sat) how to decide the value of Vce(sat) ULN 2003.
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Vce(sat) on a ULN2003 will never be as low as 0.2V. That is typical of a BJT. Darlingtons are closer to 1V.
    How much current is it going to be sinking?
     
  7. pii.inc

    Thread Starter New Member

    Jun 15, 2012
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    i use microcontroler for control uln 2003, output current from the port = 20mA.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    No, I mean how much current does the 7 segment device require, i.e., what will the ULN2003 collector current be (each collector)?
     
  9. pii.inc

    Thread Starter New Member

    Jun 15, 2012
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    current 7 segment require = 20mA
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Then Vce(sat) for the ULN2003 will be about 0.7V.
    See fig. 11 in the datasheet.
     
  11. pii.inc

    Thread Starter New Member

    Jun 15, 2012
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    thank you ron, one question more. lol.... :)
    i'll control buzzer 12v with ULN 2003 and AVR without transistor PNP, do i have to put Rb at output ULN? as i know buzzer is Z (impedance)
     
  12. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    If the buzzer is specified to run on 12V, then you won't need a resistor in series with it.
     
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