DC motor Speed control using 4093

Discussion in 'Homework Help' started by eric_s88, Jun 11, 2011.

  1. eric_s88

    Thread Starter Member

    Apr 20, 2011
    157
    1
    Hi everone,
    I have made a DC motor speed control with 4093 IC. but it doesnt work correctly. I use a 12V voltage as its supply, but when I change the value of the variable resistor, output voltage isnt beed changed. and so the speed of motor is the same.
    I better say that the output voltage is always the same of supply..
    I have inserted the schematic of circuit here..

    whats the problem :( ?
    [​IMG]

    thank you
    Eric
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,344
    Hello,

    Do you have an oscilloscope?
    Than you can measure the pulses on the output of the oscillator (pin3)
    If that is working, you can check the gate of the mosfet.
    If that is working, you can check the Vds.

    Bertus
     
  3. eric_s88

    Thread Starter Member

    Apr 20, 2011
    157
    1
    Thank U bertus
    but if there were no pulses on pin3?? what would it be then?
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,344
    Hello,

    This is basicaly the schematic of the oscillator:

    [​IMG]

    In your schematic the pins 1 and 2 are tied together.
    Also the resistor is replaced by a fixed resistor and a potmeter with diodes to have different rise and fall times.

    Bertus
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    656
    The circuit is a variable duty cycle oscillator, which applies pulse width modulation (PWM) to the motor.
    You need lots of decoupling capacitance from +V to GND. At minimum, you should have a 100nF capacitor from pin 14 to pin 7. and several hundred microfarads from the + end of the motor to the source of the MOSFET. You may need more, depending on the layout and the wiring.
    The MOSFET needs at least 10V gate drive to ensure full turn on.
     
  6. eric_s88

    Thread Starter Member

    Apr 20, 2011
    157
    1
    thank u Bertus, and Ron.
    Ron I have measured the voltage of the gate and its about 6V, whats the problem? can it be the cause of not changing the speed of motor??

    thanks
    Eric
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    656
    What are you using to measure it with?
    What was your power supply voltage when you made this measurement?
     
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