Driving MOSFET IRL540 with microcontroller signal

Discussion in 'Embedded Systems and Microcontrollers' started by Ahmed Waleed, May 10, 2009.

  1. Ahmed Waleed

    Thread Starter Member

    Mar 4, 2008
    Dear All,

    I'm trying to drive a HexMOSFET IRL540 with microcontroller output signal (5 v) for an inverter (1ph full bridge) with main supply voltage 24V and load current rating it up to 500 mA.
    But i faced a problem that the output voltage (must be = to main supply voltage) is not the desired one and it's too small (nearly 4 v).
    I asked about that and i got a strange answer...that i have to make my gate driving voltage nearly supply voltage but it was stated in datasheet that it's HEXFET (i.e. it can be driven using only logic signal 5V).


    please help me with.

    i appreciate any ideas.
    thanks in advance
  2. jpanhalt


    Jan 18, 2008
    That statement is essentially correct; in fact, you may have to boost the gate for the top mosfets (e.g., Q1) to supply + 4V to turn them on. In order to understand that, consider the situation when the diagonal mosfets starting with Q1 are turned on. Voltage drop across the load and bottom mosfet will be approximately your supply voltage minus the drop across Q1. The voltage across Q1 is very small, thus its source is almost at your supply voltage. That means its gate must be greater than the supply voltage by the voltage necessary to turn it on (i.e., 4 to 5 V).

    Search on high-side drivers for more explanation. I suggest that you use a dedicated mosfet driver for this design. Some drivers are designed for driving both high and low-side N-channel mosfets. Other drivers are for high-side P-channel and low-side N-channel.

    Finally, on my PC it was very difficult to read your schematic, so I apologize for not just using the correct part numbers in the above description.

  3. Ahmed Waleed

    Thread Starter Member

    Mar 4, 2008
    thank you john for your reply...I knew now why it gives the correct output when i used an amplifier circuit (2N2222 transistor) to amplify the gate voltage to a value more than 24v (nearly 28v).
    Thank you for the driver idea i think it'll be reliable more than my amplifier circuit.
    Best Regards