Optocoupler for driving this circuit

Discussion in 'The Projects Forum' started by FardinBiper, Sep 12, 2012.

  1. FardinBiper

    Thread Starter New Member

    Aug 21, 2012

    I am searching for a suitable optocoupler for driving the circuit shown in the attachment.
    The MOSFET is IRLB3036GPbF. I know its different from the diagram.
    This MOSFET has awesome characteristics. Low RdsON, 60V, 380W dissipation, 195A...
    The current that comes from the battery and cap is 110A. The heat loss in the resistors is of no concern here.
    My question is this: what is a suitable and inexpensive optocoupler for driving both of these MOSFETs?
    Note: supply voltage for optocoupler can be 5V, 8V, or 12V. The opto is driven with a microcontroller PWM pin at 1kHz frequency (I probably need resistor there too).

    Thank you,
  2. ScottWang


    Aug 23, 2012
    I think you need a 10K resistor connect to Vg of the MOSFET, and another pin of resistor, should be connect to GND, this will avoid that when the photo-transistor was off, the Vg will going to High Impedance, and then it could be have vibration happened, it will also affect Vd of the MOSFET.

    The LED also need a resistor for current limitation.
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Since you are using PWM, you need to drive the gates of the FETS with a high-speed, high-current gate driver. Big FETS have lots of gate stored charge/gate capacitance. It takes a gate driver IC with a max drive current of an AMP or so to quickly turn-on, and then just as quickly to turn-off the FETS, otherwise you will blow them up because of dissipation that takes place while they are switching....
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
    +1 to MikeML's suggestion of a gate driver. If you use one of International Rectifier's drivers you also won't need a optocoupler. Something like this- http://www.irf.com/product-info/datasheets/data/ir4426.pdf

    Also be wary of the claims on the data sheets. That mosfet "package" is limited to ~75 watts, no matter what the claims are.