irlz44n not fully open using 3.3V Arduino

  • Mod

    I have a project with a 3.3V sensor. To avoid trouble with logic levels, I use a 3.3V Pro Mini.

    In addition to reading the sensor, the Pro Mini handles dimming of a RGBW led stripe through irlz44n MOSFETs. However, the mosfets do not fully open at analogWrite(PIN, 255), nor at digitalWrite(PIN, HIGH).

    According to the datasheet, VGS(th) / Gate Threshold Voltage is 2V max. I thought that meant that the mosfet would be fully open at >2V?

    The mosfets do open fully if I use a 5V Pro Mini. They also open fully if I use a 3.3->5V logic level converter for the pwm pins.

    Does anyone know why this happens?

    Can anyone recommend a mosfet that works better for 3.3V (preferable as cheap and low on-resistance as the irlz44n)? I need to handle 2A at 12V.

  • Hardware Contributor

    Many mosfet does not open fully on 3,3V. You have to check graph in datasheet when choosing mosfet.
    You can pull gate high with a resistor to 12v and use a npn transistor to pull it low.
    But that makes it default on. If sensor node fails all leds will be at 100%.
    My ledmodule uses IRLR2905 and is powered by a 5v promini.

  • Contest Winner

    I tested this n-channel mosfet. It works fine (3.3v),

  • Nice... Ordered yesterday some IRLZ34n for my project... D'Oh!

  • Hardware Contributor

    I think I was using some of these for my rgbw controller and they seem to work just fine for me. As I switched to smd parts I can't really help you though 😞 My only idea would be to control them via some (smaller) transistor(s) that can be fully opened with 3.3V (or just redesign).

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