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FET as a switch and FPGA ?

Discussion in 'Homework Help' started by sstbrg, Jun 21, 2009.

  1. sstbrg

    Thread Starter Active Member

    Nov 29, 2008

    Well, my task is to switch 28 volts to activate a 28v/50mA dc lamp using FPGA.
    Relay is not an option. One of the lamp's pins must be connected directly to the ground.

    My idea is to take an optocoupler (without base connection for now) and connect it to the 3.3v output of the FPGA (with some resistor in series). Then the collector pin will be connected to 28v (or 5v), the emitter pin will be connected to the ground through a 100k resistor. The output will be on the 100k resistor, connected to the gate of a N-channel JFET or MOSFET. The drain of the FET will be connected to 28v, and the lamp will be connected between the source and the ground.
    This is to ensure that there is no possible relationship between the FPGA and the FET.

    Also, is it possible to use a p-channel [mos/j]fet for this task?
    If so, how? If not, then why not?

    Thanks for all the fish :)
    Last edited: Jun 21, 2009
  2. Bernard


    Aug 7, 2008
    Just something to think about.