Questions about the IC ULN2003?

Discussion in 'General Electronics Chat' started by samy555, Dec 13, 2015.

  1. samy555

    Thread Starter Active Member

    May 24, 2010
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    http://www.engineersgarage.com/electronic-components/uln2003-datasheet

    I read: (….. It contains seven open collector Darlington pairs with common emitters.) What does he mean by saying common emitter? Is he mean all emitters of the 7 Darlington pairs are all connected together and with the common ground (pin #8)?



    How to use pin #9?


    What the difference between driving a 12V relay using this IC or using a simple suitable transistor?


    Thank you very much.
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In the datasheet from allegro, the use of the chip is more clearly given.

    Bertus
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    This chip is just a simple way to connect seven transistors to your circuit. All seven have the emitter connected to ground. Essentially transistor switches with load connected between collector and Vcc.

    Pin 9 can be used to connect a reverse-biased diode across inductive loads. It can be left unconnected if not needed.

    I recently used one of these when I needed to drive a 7-segment common anode LED with a cd4511. The cd4511 is intended to drive a common cathode 7-segment. The UL2003 essentially inverts the signal and can drive higher currents than the logic chip.
     
  4. eetech00

    Active Member

    Jun 8, 2013
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    The emitter of the second transistor of each Darlington pair is connected together and brought out on pin 8.
    When driving relays, pin 8 is usually connected to ground.
    If not used, Pin 9 is connected to V+ or not connected. I've used this pin as a lamp test function when driving LEDs.
    You can also use it as transient suppressor when driving relays. But I would connect a discrete diode across each relay anyway.
    You can build the same circuits with discrete components without using a darlington pair. But this IC gives you a compact package of 7 drivers already designed for driving up to 20-300ma loads on each output..

    Be sure to choose the correct IC. Each is designed to interface with specific types of devices. For example, ULN2004A is designed for CMOS devices with voltage range of 6-15v, while ULN2003A is designed for TTL or 5v CMOS devices. Its all in the datasheet.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Also the ULN2803 covers 8 drivers which are often handy if using 8 bit data.
    Max.
     
    GopherT likes this.
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I was quite surprised that the ULN2003 had only 7-channels. It worked out perfectly for my use on 7-segment displays but I couldn't imagine what other purpose 7-channels would bring - I would have thought 8 would be a more convenient number.
     
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  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Keeping the part in a 16 pin package was a big deal at the time. Also, many industrial applications are not 8-bit data bound. Over decades, my use of the 2003 vs 2803 is around 10:1.

    ak
     
  8. MaxHeadRoom

    Expert

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    Mine has been the opposite experience, using 8 port processors and Servo motion controllers with 8 I/O ports, these date back to the early 80's.
    Max.
     
  9. ScottWang

    Moderator

    Aug 23, 2012
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    The total current of ULN2003 is 500 mA, whatever one channel or all 7 channels, but for the power dissipation, you better just using it less than I=500mA * 1/3 = 167mA.
     
  10. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    I've chewed up a lot making logic gates out of them. 50V, 1/2A, input and output transient protection built in practically indestructible, perfect for automotive applications where you need a little combinatorial glue.

    ak
     
  11. samy555

    Thread Starter Active Member

    May 24, 2010
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    To
    Bertus
    GopherT
    eetech00
    MaxHeadRoom
    AnalogKid
    and
    ScottWang
    thank you very much
     
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