Power Mosfet Selection

Discussion in 'General Electronics Chat' started by pilko, Oct 18, 2011.

  1. pilko

    Thread Starter Active Member

    Dec 8, 2008
    Hi All,
    I am in the process of sourcing a Power Mosfet for 20KHz PWM driving a 90V: 0.5HP permanent magnet shunt motor. I will be using a driver.
    I have found a STP30NF20 (data sheet attached).
    It looks good to me because of the following specs:

    VDSS = 200V
    ID = 30A
    RDS(on) = 0.075 Ohms
    Total Gate charge = 38nC

    Can some one tell me if it is suitable for motor driving. The reason I ask is because of the following description in the data sheet.

    ■ ​
    Switching applications

    This Power MOSFET series realized with
    STMicroelectronics unique STripFET process has
    specifically been designed to minimize input
    capacitance and gate charge. It is therefore
    suitable as primary switch in advanced highefficiency​
    isolated DC-DC converters

  2. crutschow


    Mar 14, 2008
    What is the maximum motor current?

    It looks suitable for your application.

    Make sure the driver can charge and discharge the total gate charge rapidly enough to give short rise and fall times for the gate voltage and minimize switching losses.
  3. pilko

    Thread Starter Active Member

    Dec 8, 2008
    Thanks for the response crutschow.
    The full load current in my app is 7 Amps; The inrush is 18A >>>7A in less than 1 Sec.

  4. JDT

    Well-Known Member

    Feb 12, 2009
    You should use a MOSFET driver that can quickly deliver large currents to charge and discharge the gate capacitance.

    Also important is having an "undervolt lockout" so that you never partially turn on the MOSFET - on power up or during loss of power for example.

    A partially switched on MOSFET with only a small gate voltage will be instantly destroyed due to internal power dissipation or secondary breakdown. I know from experience!

    The gate driver IC MC33152 (for example) has this built-in.
  5. pilko

    Thread Starter Active Member

    Dec 8, 2008
    Thanks JDT.
    I am now trying to calculate the required gate driver current from I = Q/dT,
    but I am unsure what to use for dT. The data sheet quotes:

    Turn-on delay time
    Rise time
    Turn-off delay time
    Fall time

    Help would be appreciated