PWM Motor speed contorller, MOSFET getting hot

Discussion in 'The Projects Forum' started by wstay90, Mar 9, 2013.

  1. wstay90

    Thread Starter New Member

    Mar 3, 2013
    4
    0
    Hi,

    I have a PIC16f877A controlling the DC speed motor.
    The motor is basically 12V motor rating of 8W(around 600mA).Actually it is a submersible water pump which commonly used in Aquarium.
    The mosfet that I'm using is K1300.
    When i ask the electronic shop for IRLZ14, they didnt have, so they just find
    a replacement part number from the book which is K1300.

    When running the circuit,It takes few second for the motor to actually start pump the water and
    the MOSFET get quite hot which is impossible for me
    to touch after around 10 seconds. It is a T0-220 Package. Im running at 5Khz.

    I'm from Malaysia, getting some other model MOSFET will be hard.
    is it the wrong mosfet that im using ? or thats something wrong with my circuit I uploaded my schematic below. Or is it the gate-voltage(4.5V) for the K1300 is not enough and therefore produce so much heat.
    Thanks and Appreciate
     
    Last edited: Mar 9, 2013
  2. antonv

    Member

    Nov 27, 2012
    149
    27
    I haven't looked at the MOSFET data but for sure don't drive it through a 1k resistor. The MOSFET probably never gets time to turn on completely.

    What is your PWM frequency? You may need to add a MOSFET driver circuit to make sure the transistor turns on and off completely.
     
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    A 2SK1300 Mosfet looks like it's nearly fully on with 4.5 v gate drive.
    So, try reducing the gate resistor to 10-47 ohms.
    You could try reducing the PWM frequency. What is the duty cycle or the on time vs off time of the PWM signal?
     
    wstay90 likes this.
  4. antonv

    Member

    Nov 27, 2012
    149
    27
    The issue may be that the 25mA that the PIC can source into the MOSFET gate is not enough current to turn it on fast enough.

    Also, a small heat sink may be a good idea.

    The transistor is probably a 2SK1300 MOSFET.

    Do you have access to an oscilloscope?
     
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  5. wstay90

    Thread Starter New Member

    Mar 3, 2013
    4
    0
    At that time i was running at 5Khz frequency;
    setup_timer_2(T2_DIV_BY_16, 61,1) 20Mhz HS oscillator.
    and set_pwm2_duty(61) which is 100%; correct?
    so i might lower to 1.2Khz(Lowest) and trying lower and hopefully adding heatsink will help.

    the gate resistor is the 1k or the 10k ?
    Later i will try measure again using multimeter at the gate-source Voltage. see whether it is around 5V.
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    You also don't need R2.
     
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  7. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Sorry, the series gate resistor, the 1k. :)
     
    wstay90 likes this.
  8. wstay90

    Thread Starter New Member

    Mar 3, 2013
    4
    0
    Ok thanks, In what cases should the R2 is needed ?
     
  9. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    Only if you have a floating input for some reason.
     
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  10. wstay90

    Thread Starter New Member

    Mar 3, 2013
    4
    0
    Could the 1N4007 diode playing the role of heating up?
    as this is not rapid diode.
     
  11. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Take a look at this.
     
    Last edited: Mar 10, 2013
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