Using a photologic slotted photo optical switch to drive a mosfet

Discussion in 'The Projects Forum' started by gordonfrench, Sep 27, 2016.

  1. gordonfrench

    Thread Starter New Member

    Sep 23, 2016
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    I am trying to use this slotted sensor to run a load on a mosfet. The switch is a buffer with totempole OPB980T11Z. The driver is a MIC4452
    I am using a 5v supply for the switch and driver Vs and a 12v battery to supply the load at the mosfet.
    I assume the % wires on the switch gets connected : Red- Anode to Vs Black - Cathode to Ground White - Vcc to Vs Blue - Output to driver input Green - Ground to Ground
    I am able to provide a pull up resistor to the driver input to activate the on state and then use a ground to shut down or on off.
    But I can not get the switch to operate. I can't seem to find a circuit example to help me. Dose anyone know what I am missing here?
     
  2. wayneh

    Expert

    Sep 9, 2010
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    3,061
    Are the 5V and 12V grounds connected?
    When you used your pull-up resistor, did you apply it to the driver to simulate the switch output, or directly to the gate of the MOSFET?

    Have you measured the output voltage of the switch?
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Why are you using a driver?
    You should be able to drive the MOSFET directly from the opto.
     
  4. gordonfrench

    Thread Starter New Member

    Sep 23, 2016
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    Yes both grounds are connected!
    Yes I am able to get the driver to control the mosfet.By shorting the input to ground or 5v through 10k resistor.
    When I measure the voltage output of the switch I get 0 and 4.9v when I trip the slot.I also checked with a LED from output to ground , It operated but very weakly.I tested several switches to rule out bad switch.
    I even tried as suggested connecting the output of the switch direct to the mosfet, it could not turn on but had strong signal to shut down.
    I bought several new switch to make sure it was not the switch.
    Switch grounds are connected to ground as seen in pic.
    I am sure it is not due to bad connection I have checked 20 times.
    I used this switch before to drive a mosfet, it worked then, it's driving me nuts, it should work.
     
  5. gordonfrench

    Thread Starter New Member

    Sep 23, 2016
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    I am only using a light bulb to test the switch. In the end I will be using it to drive a pulse motor. The switch needs a driver for protection.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You need a 300Ω resistor on the A pin and the K to common, Then K can connect to GND , as it is push-pull out you do not need a pull up and should see the 12v swing on the output when triggered.
    Max.
     
  7. gordonfrench

    Thread Starter New Member

    Sep 23, 2016
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    Max, Thank you for replying. I don't understand what you mean " the A pin and K to common. Would you clarify?
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    A & K are the anode and cathode of the emitter diode as shown on the OPB980 sheet.
    K to common or GND
    Max.
     
  9. crutschow

    Expert

    Mar 14, 2008
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    Protection from what?
     
    wayneh likes this.
  10. gordonfrench

    Thread Starter New Member

    Sep 23, 2016
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    Thank you again Max! Your right the Anode requires a resistor. Now my circuit works using the supply voltages as described. I was using this before to run a pulse motor. But my voltage supplies were different. 7.5v low - driving 180v high
    What formula did you use to size the resistor?I found it last time by trial and error.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The max LED current as per the spec sheet.
    Max.
     
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