ULN2003 operation principle question

Discussion in 'General Electronics Chat' started by mdemirst, Jul 20, 2012.

  1. mdemirst

    Thread Starter New Member

    Jul 20, 2012
    2
    0
    Yesterday I was trying to drive 3 phase HDD motor with ULN2003 but I couldn't make it working. Because I learned it is not a current source. It just works as a switch. Am I right?

    So, in order to use it with any device, I should connect the first pin of device to positive voltage and the second pin to ULN2003 so that it works.

    My question is about working principle of ULN2003. It says there is a inverting buffer connected to input pin of ULN. How does this buffer work as a switch for letting current to flow?
     
  2. rfredel

    New Member

    Jan 23, 2011
    25
    3
    Hello mdemirst,

    look for the datasheet on page 3.

    http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00001244.pdf

    Here you see, that the ULN2003 ist an amplifier with NPN - darlington transistors and open collector.

    If you put a positive voltage (input of buffer) to the base the transistor will open. The diode from collector to COM is a free wheeling diode for inductive loads. It must connected to positive supply voltage of your motor. the other end of the coil must connected to collector.

    So it will be function.

    Regards

    Rainer
     
  3. mdemirst

    Thread Starter New Member

    Jul 20, 2012
    2
    0
    Thank you.. Datasheet answered well my question. They use darlington transistor pairs. Input is connected to the base of first transistor which opens the gate.
     
  4. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    I don't like the terminology you have used.
    "Open" has a very precise meaning in Electronics,meaning "open circuit"--in other words,non conducting.
    A transistor when turned on is very close to the opposite condition.

    A ULN2003 is simply a Darlington transistor array.
    Each individual Darlington will turn on & conduct when a positive voltage is placed on the base,drawing current from the collector supply,through the load,in this case a motor.
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    "Open Collector" is a very common term used to indicate that the collector of the output transistor is not connected internally within the IC to anything else and is "OPEN" to the outside world for use. If you don't like the term and the way it is used, you will have a lot of re-writing to do in updating all of the data sheets that use it.

    http://www.google.com/webhp?rlz=1C1....2,or.r_gc.r_pw.r_qf.,cf.osb&biw=1360&bih=607
     
  6. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    I realise my meaning was unclear,

    Please read rfredel's posting again.

    What I was referring to was this comment:

    "If you put a positive voltage (input of buffer) to the base the transistor will open."

    This implies that the transistor is turned "ON" (effectively "short cct") without the application of a positive voltage,& will "open" (turn"OFF"),when such a voltage is applied,in other words,the opposite to its real function.

    I was attempting,apparently unsuccessfully, to prevent confusion on this point.

    I am quite familiar with the meaning & usage of the term
    "Open Collector",& was not referring to that term.


     
  7. rfredel

    New Member

    Jan 23, 2011
    25
    3
    Hello vk6zgo,

    sorry, if I made a mistake in writing.

    I come from Germany and I have to translate my text from German to English. In German it is the write discription for the function of ULN 2003.

    Sorry agian

    Regards

    Rainer
     
  8. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Your English is a lot better than my German.;) which is ZERO!! Welcome to the forum.
     
  9. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    Hi Rainer,
    Sorry if I was a bit over-critical,I was just a bit worried the newbies might get confused.
    Come to think of it,even if they did,it would be a good learning experience.:D

    Cheers,

    VK6ZGO
     
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