BJT Motor Amplifier

Discussion in 'The Projects Forum' started by Mazaag, May 1, 2007.

  1. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
    255
    0
    Hi guys,
    just a quick question.

    If i am using a BJT common emitter amplifier to drive a motor, where do i connect the motor? to the collector?

    thanks for your help guys
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,135
    1,786
    I believe you are a few facts short of a solution.
    What kind of motor?
    What's the other end connected to?
    What are the supply volatges?
    Where did you get the idea you could do this?
    Are you open to alternate suggestions?
     
  3. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
    255
    0
    -DC motor
    - I don't know what you mean by "the other end"
    - The motor is a 18v motor, not sur eof the exact current specs
    -I am open for any suggestions


    okay so ehre's the full story

    I have a controller implemented on MATLAB, and I would like to control the dc motors. I am using an NI-Daq to output voltages from Matlab to the motor, however, it doesn't source enough current to run the motor ( voltages from -10 to +10 , and maximum current of approx 5ma)

    as far as i know, the motor requires both 18v and enough current to spin, but I have no idea how to get enough current and voltage from my daq .

    Insert suggestions here...
     
  4. Salgat

    Active Member

    Dec 23, 2006
    215
    1
  5. Papabravo

    Expert

    Feb 24, 2006
    10,135
    1,786
    Progress.
    Does the DC Motor have brushes? or is it a brusshless DC Motor?
    In order to function a DC Motor with brushes MUST have more than one connection. One end is connected to the "amplifier" and the other end is connected to ground. When the amplifier outputs +Voltage the motor runs in one direction. When the amplifier outputs -Voltage it runs in the opposite direction. Does that sound like what you have?

    Neither a Common Collector, nor a Common Emitter Amplifier all by itself will be suitable for your purposes. You need something like a class AB push-pull amplifier OR a Bridge Amplifier if you want the two motor leads to float as opposed to one of them being grounded.

    Unless you can determine an approximate starting and running current for your motor this project is doomed to endless trial and error. You are correct about one thing though: 5 mA from a DAC will not start or run anything but the smallest of toy motors.
     
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