General purpose Logic to Power switch

Discussion in 'The Projects Forum' started by ianicr, Sep 13, 2009.

  1. ianicr

    Thread Starter New Member

    Sep 13, 2009
    2
    0
    Hi
    I have several projects underway but all have common factors - logic level supply and high(ish) level outputs.

    The logic is from Basic Stamps at the moment and the outputs need to drive Nitinol wires (muscle wire), stepper motors or cree high power LEDs. Operating frequencies are unlikely to exceed 200Hz.

    I was hoping to make 'universal' boxes (one per coil for the steppers) to fit between these devices so that I can just re-use them in the future.

    As I work in a school, the main sources of low volts tend to be chunky transformer units with full wave rectification and nothing much else. If needed I could scavenge the PSU out of a PC to give a cleaner source of power.


    The circuit that I think would suit all of these is pretty much the one shown in figure 10 at the bottom of page 5 of http://www.vishay.com/docs/81227/81227.pdf but using a diode-protected power MOSFET instead of the IGBT.(I got some IRF540 Power Mosfet 28A 100V at 25p each which I hope to use). The only addition that I would make to the circuit is a current-limiting resistor for the muscle wire and the LED projects in series with the load and perhaps a resistor and/or zener diode to protect the input LED from over-voltage.


    There seem to be several optocoupler gate driver chips and I can't see much difference between them at the frequencies that I am using. Fairchild FOD3180 (2A output), FOD3181 (0.5A output) as well as some made by NEC and others.

    Somehow, this circuit seems too simple! Have I missed something?


    I would greatly appreciate any insight you can give me on this, and I appreciate your time spent.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    If your needs are all a matter of DC current control, then a device like a IRF530 FET might do for everything. The requirement to turn one on is to bring the gate voltage 10 volts above the source, and pull it down to the source potential to turn it off.
     
  3. ianicr

    Thread Starter New Member

    Sep 13, 2009
    2
    0
    Thanks Beenthere, but I'm not sure what you're saying.

    The chips that I'm proposing give optoisolation - to protect the Stamp - and boost the 5V from the Stamp up to whatever is needed to drive the FET.
    I'm not confident in understanding the differences between my IRF540 and the IRF530 that you suggest.

    In any case, I will need some circuitry to boost the 5V from the Stamp up to the 10V that you suggest.

    The Fairchild optocoupler gate driver chips may not be the cheapest way of doing this, but they certainly seem simple! Or am I missing something.

    Thanks

    Ian
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Got ahead of the question. The optoisolation may be a bit unnecessary, but can't hurt. The outputs can place any voltage up to 20 on the FET gates to turn them on.

    Your big decision seems to be choosing a connector to use between the microcontroller and the various control modules.
     
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