optocoupler circuit controlling 24V

Discussion in 'General Electronics Chat' started by mcn14, Mar 5, 2013.

  1. mcn14

    Thread Starter New Member

    Mar 5, 2013
    3
    0
    Hello

    I have a 4n35 octocoupler circuit with 5v input (on the LED side) controlling a 24 V (on the transistor side) , I am having problems calculating the resistor values for the base and the collector.

    many thanks
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Controlling a 24v? 24v what? What are you trying to control on the transistor side? The current requirements of the device on the transistor side will help determine the resistor values.
     
  3. mcn14

    Thread Starter New Member

    Mar 5, 2013
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    0
    The output side of the transistor is connected to a Mosfet gate, in order to drive a H bridge.
     
  4. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    These are not particularly fast devices so look at the frequency response versus load resistance curves to see if you can fit your application if you are attempting anything but DC application. Charging up the gate of the mosfet will also slow you down as it will look like a capacitance attached to the output.

    There are graphs in the datasheet that reference Rload, which is the resistor attached to the collector.

    Do you have a schematic of your circuit? Without any other information you may have some trial and error, select resistors to give you 10 mA of forward and collector current and go from there...
     
  5. nigelwright7557

    Senior Member

    May 10, 2008
    487
    71
    You could use a TC4420 mosfet gate driver from the opto.
     
    mcn14 likes this.
  6. mcn14

    Thread Starter New Member

    Mar 5, 2013
    3
    0
    Many thanks for your help, I have tried a range of resistors today however I was unable to get the required current to drive the FET's. I think I have to invest in a MOSFET Driver chip.

    The thing is I currently have three parts to my circuit the PWM logic which is coming from a PIC, the octocoupler circuit (which is not working) and the H bridge (which is working) my problem is linking the 5V pwm signal to the H bridge gate which requires 24V in order to function.
     
  7. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    It would really help if you could post a schematic of what you've done so far.
     
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