Darlington transistor question

Discussion in 'The Projects Forum' started by DougB, Sep 11, 2010.

  1. DougB

    Thread Starter New Member

    Sep 11, 2010
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    0
    I have a schematic for a cct that is to be used for thermal electric cooler(TEC) regulation on A CCD camera kit that I am building. It utilizes a AD822AN op amp and an ECG2443 darlington transistor to supply the appropriate power to the peltier module. Nominal input to the collector is 8.5 VDC. Output I am not sure of, but it has to be less than 7.5VDC( Limits of the TEC).
    My understanding of darlington transistors coupled with op amps is to provide a more stable voltage output while allowing the current to be varied depending on the bias voltage applied to the base, but I could be wrong.

    The cct as designed limits the current and voltage to the TEC to prevent overheating of the device. I would like to be able to use 12 VDC instead of the
    8.5 VDC input. What would be the result of the change in input voltage only?

    If this could cause me grief, what would I need to do to drop the voltage down from 12 to 8.5 and hopefully hold it there with increasing or decreasing loads placed on the system by the TEC? Max current is about 2.5 amps.
     
  2. campeck

    Active Member

    Sep 5, 2009
    194
    3
    Could you post the schematic?

    And I'm curious as to why you are cooling the ccd. Astrophotography maybe?:D
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Please check the part number. I can't find any data on an ECG2443 Darlington. If that is the correct part number, supplying the schematic and current requirements of your TEC will help a great deal in locating a suitable substitute. NTEinc acquired ECG quite a while ago. Perhaps you meant ECG243, which cross-references to NTE243?
    Datasheet:
    http://www.nteinc.com/specs/200to299/pdf/nte243.pdf

    The NTE243 is rated for 80v, up to 8A continuous current, in a TO-3 package.
    You might substitute a 2N3055 being driven by a 2N2222.
    Newark, amongst other vendors, stocks the NTE part: http://www.newark.com/jsp/displayPr...U-OTH&s_kwcid=TC|14641|nte243||S|b|5199926661

    Depending on load, a Darlington will generally have a Vce anywhere from 0.7v (light load) to ~2.5v (heavy load) before its' power dissipation ratings are exceeded.
     
  4. DougB

    Thread Starter New Member

    Sep 11, 2010
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    Will post a schematic later once I figure out how to do that.

    Good guess as to why I need the CCD cooled, 100% correct.
     
  5. DougB

    Thread Starter New Member

    Sep 11, 2010
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  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    OK, so about the same as a TIP142.
     
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