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Logic mosfet pwm

Discussion in 'Microcontrollers, Programming and IoT' started by turbogt16v, Apr 2, 2018.

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  1. turbogt16v

    turbogt16v

    173
    4
    Mar 27, 2015
    Hy,i got problem with led not powering when it is connected to logic mosfet and Arduino.when i touch the connections i get some power.
    Do i need to put diode or resistor on gate,or what is the solution
     
  2. Bluejets

    Bluejets

    4,607
    977
    Oct 5, 2014
    Circuit...?
    No idea what you mean by "when I touch the connections I get some power".
     
  3. Kiwi

    Kiwi

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    85
    Jan 28, 2013
    Do you have a diagram of your circuit?
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    11,160
    2,548
    Nov 17, 2011
    Which logic MOSFET? Which Arduino?
     
  5. turbogt16v

    turbogt16v

    173
    4
    Mar 27, 2015
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    11,160
    2,548
    Nov 17, 2011
    What color is the LED? depending on color the 3 V from the regulator may not be enough.
    You should also provide a current limiting resistor. See our resource about driving LEDs.
     
  7. Alec_t

    Alec_t

    2,935
    799
    Jul 7, 2015
    You should really be driving the LED with a controlled current, not a fixed voltage.
    What is the rated maximum current for that LED?
    Can your power supply cope with that current?
    Is the LED mounted correctly on a BIG heat-sink?
     
  8. Wollowstone

    Wollowstone

    18
    4
    Mar 26, 2018
    The link that you supplied for the LED specifies that it need 300 mA, which is too much for the Arduino (for each GPIO, the maximum is 40 mA, for a total of all GPIO not exceeding 200 mA, unless you have a special board...). Try using an independent power source as source for the regulator. If green or blue LED, you need more than 3V. The link you supplied indicates that for Red, you have more voltage than required (2.4 to 2.6V). With 5V at the grid, with 0 V at the source pin, this NMOS could handle a max of 70 A from its drain to its source pin, so this is surely not a problem here. Since there is almost no current ( at very low frequency) through the grid pin, adding a resistor there won't do much. The Arduino may also have a problem to sink 300 mA (it should handle 400 mA, in total, so who knows... ), so plugging the voltage regulator to an independent power source could also help there too. If the LED does not turn off as soon as the Arduino logical output asks it, you may have to add a pull down resistance to the gate, though, but that resistance won't help it lighting the LED on, as your problem seems to be (and NOT to turn it off).
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

    11,160
    2,548
    Nov 17, 2011
    That's why the op has a power MOSFET in between arduino and LED. The control of the LED power via a MOSFET is basically o.k.

    The 3V regulator needs to be able to deliver the current for the LED. Plus current limiting is required as mentioned above.
     
  10. Wollowstone

    Wollowstone

    18
    4
    Mar 26, 2018
    True, but the current for the regulator, its comes from the Arduino which is limited to 200 mA from its 5V pin ( and 40 mA if it comes from a GPIO pin). (Unless it is a special board.) https://playground.arduino.cc/Main/ArduinoPinCurrentLimitations

    Should try without any other component, just the regulator and the LED, no NMOS, to see if it lights on the LED.
     
    Last edited: Apr 3, 2018
  11. Bluejets

    Bluejets

    4,607
    977
    Oct 5, 2014
    No, regulator is being driven from 5.1v supply.
    Not a real brilliant drawing though.

    Hope the 5.1v is not from the Arduino regulator.
     
    Last edited: Apr 3, 2018
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