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Help for circuit design...

Discussion in 'General Electronics Discussion' started by makarand, Dec 16, 2016.

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  1. makarand

    makarand

    2
    0
    Dec 16, 2016
    HI guys

    I am working on a PLC whose output is in sink mode(so o/p is not generated till plc is connected in sink mode).Hence I have to extract the required PWM output from PLC using some kind of PNP transistor .The sink type output connections for PLC are as in the following figure . The output on PLC is 24v and also the battery in sink circuit is 24 v(available on plc see fig)

    The PWM generated is of 24V and is to be used to drive a Sg-90 servo which requires 5V output so i have designed following circuit and explained the connections in respect to PLC. Target is getting 5v pwm (extracted from PLC).But PNP transistors available can't withstand Vbe over 7-8V.In this Case the Vbe is 24 v (as plc o/p goes low).so the transistor gets shorted easily.

    Mosfet also can’t be used as max gate-source voltage is only around 8V.

    Major problems

    1)servo has pwm port, power,GND

    Hence I can’t give PLC’s PWM to the servo by using the resistor divider network as sink type of circuit is not created.

    2)cant reduce the PLC’s 24v o/p and external 24 V supply

    Please suggest me some other things in place of the transistor.

    Advanced Thanks for the Help…….!!!!!!!!!!!!

    sink o/p image:https://postimg.org/image/ojteu7ay9/[​IMG]

    transistor diagram:https://s24.postimg.org/5j1c5vb0l/pnp.jpg[​IMG] [​IMG]
     
  2. Minder

    Minder

    3,101
    664
    Apr 24, 2015
    What is the nature of your PLC? Is this a commercial/industrial PLC in the meaning of the word?
    Have you looked at a Mosfet in place of a bi-polar transistor?
    The nature of the output of industrial PLC's can vary from relay contact to sink or source solid state.
    M.
     
  3. makarand

    makarand

    2
    0
    Dec 16, 2016
    The plc is of industrial type.Its mitsubishi FX-5u. And the output are transistor types(sink mode).
    The max gate-source voltage of mosfet is only upto 8v .
     
  4. Minder

    Minder

    3,101
    664
    Apr 24, 2015
    Not really, there is from logic level gate type and up to a typical 20v max, that should be simple to do with a gate pull up resistor and 20v zener or just a simple resistor divider..
    I use the FX series of PLC.
    M.
     
    Last edited: Dec 16, 2016
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