MOSFET Gate Driver Circuit Help

Discussion in 'The Projects Forum' started by weidman2, Nov 4, 2010.

  1. weidman2

    Thread Starter New Member

    Oct 25, 2010
    I am trying to create a circuit that takes a PWM input from a microcontroller and controlling a IRF740B MOSFET using a FAN7382 MOSFET driver. I have gotten all of the parts of the circuit to work except for the MOSFET driver. I am getting no voltage output when testing it. Does this have anything to do with me only having a single MOSFET? Any help would be appreciated. I attached my complete circuit.
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    irf2108 Datasheet

    Why is the driver only powered with 7V to Vb, when it is capable of 20V, and there is a 15V supply near?

    Having LIN floating appears to be OK, as there is a 5k pullup internally so the output will be low.

    Try a new page with just the mosfet driver the HV Circuit and a logic level square wave input to see if that works.
  3. SgtWookie


    Jul 17, 2007
    Your schematic is rather confusing, as you have wires running everywhere, and some make a number of unnecessary bends. You also have your voltage sources in odd orientations.

    Try to keep in mind a few general standards for drawing schematics:
    1) More positive voltages towards the top of the drawing, more negative towards the bottom.
    2) Inputs come from the left, outputs go towards the right.
    3) Use node labels (Vcc, Vee, Vdd etc) and ground symbols rather than running such wires all over the place.

    Something odd is going on with your supply voltages; for example, you have the negative side of V3 grounded, but the positive side only measures 2.277V when it's supposed to be 7v? Similar thing with V5, it should be 15v on the positive side instead of 4.879v. Did you give those voltage sources a high internal resistance?

    You have C2 as 1nF. That is your boost cap for the IR2108. It should be at least 100nF (0.1uF) or larger; more preferably a 47uF and 0.1uF cap in parallel.

    Ground the LIN pin.

    A 1N4149 was a poor choice for D1; very low current rating. It needs to be a fast recovery or Schottky diode.
    I don't know what frequency you are planning for this thing to operate at, but 2uH is a VERY small value for L1 - you'd have to be operating in the MHz range.

    C1 is far too small.

    You have no feedback to detect the voltage across C1/R5. How will you know when it's charged up enough?

    There is no current limiting resistor for the IR emitter side of the 4N25; U1.
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    The L_{IN} is an inverted input, on the datasheet, it is \overline{L_{IN}} There is an internal pullup to +V.