Whats the best way to drive a power mosfet from a uC PWM signal?

Discussion in 'General Electronics Chat' started by Subterranean, Dec 7, 2010.

  1. Subterranean

    Thread Starter New Member

    Jul 27, 2010
    This seems a fairly simple topic but I couldn't find a comparative view anywhere so I apologise if its a simple answer.

    I am looking to drive a couple of power mosfets in parallel (probably IRFP2907) from a PIC microcontroller. I realise that the mosfets need at least 10v to fully turn on so I will probably use a 12v rail that I'm already planning to have in the project.

    What is the best method to drive the power MOSFETS from the microcontroller's 5v output? I have thought of 3 different options but I'm not sure if any of them are immediately the obvious choice:

    1. Use a smaller MOSFET that turns fully on at 5v to supply the 12v to the power MOSFET gates.

    2. As above but use an op-amp.

    3. Use a mosfet driver IC.

    I would have thought option 3 would be the best, given that it sounds like a mosfet driver is designed to do exactly what I'm looking for, except that I can't find any noob friendly information about how they work and how I would integrate one between a uC and a power mosfet. If anyone can help with this please do.

    The first two options seem simple enough, but perhaps I would struggle with controlling the gate capacitance of the power mosfet?

    Any help would be very appreciated.
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    A dedicated driver is probably your best bet. There are lots of options. Look up MC34151/ MC33151 as an example. The datasheet has several pages on layout and operation. It will take logic input.

  3. retched

    AAC Fanatic!

    Dec 5, 2009
    You can get power MOSFETS that have LOGIC level gates (5v)

    For speed, you will want to use a gate driver.

    I like these:

    Clare IDXF604

    Logic input. 10nS rise times.

    It depends also, if you are doing high or lowside switching.
    Last edited: Dec 7, 2010
  4. Subterranean

    Thread Starter New Member

    Jul 27, 2010
    Thanks for the info on mosfet drivers, it sounds like I will use one of those.

    But theres still one simple thing I don't understand, how would using the mosfets in a high or low side configuration make a difference to how the driver needs to operate? Since you can get high and low side drivers I assume it does matter but I dont see how the drivers themselves would be different for the different switching methods. Or is it a bit complicated.

    Thanks again.
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
    With a high side mosfet you need to bring the gate voltage up to 10V higher than the source voltage. The driver and a few other components let you do this.

    With a low side mosfet you just need the gate voltage to be 10V, because the source is at '0'V or circuit ground.

    You probably already know what makes a mosfet high or low sided, but if not this is the difference ---
    High side - the load is after the mosfet, between mosfet source and "ground'.
    Low side - the load is between the positive voltage point and the drain of the mosfet.
  6. SgtWookie


    Jul 17, 2007
    That would turn a gate ON, but you'd need more circuitry to turn it OFF.