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Block Circut With Small Signal

Discussion in 'General Electronics Chat' started by ke7doy, Apr 15, 2008.

  1. ke7doy

    Thread Starter New Member

    Apr 15, 2008
    I need a sort of a reverse relay. It needs to block the current (about 500ma 5.5vdc) flowing in a circut as long as there is 2ma 1vdc signal present. It would be best there was no power consumption other than the signal when the circut is blocked. I can't search for an answer because I don't know what the parts.
    Thank You
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    Try "JFET" as a search term. Don't know if you'll find one for your combination of needs, but it's worth a try.
  3. Caveman

    Senior Member

    Apr 15, 2008

    This would be accurate, but may be more than you need. U1 is a comparator, not an opamp.
  4. SgtWookie


    Jul 17, 2007
    two small problems.

    1 - many comparators have open-collector outputs, which require a pull-up resistor in order to actually provide an output signal.
    2 - mosfets typically require 10v to fully turn on.

    so, in order to make your circuit work, it will require a pullup resistor on the output to a supply of 10v or 12v, of 1k or 1.2k ohms for a 10ma current.
  5. Caveman

    Senior Member

    Apr 15, 2008
    1. Push pull comparators are easily available (ie, mouser/digikey).
    2. Logic level mosfets (Vgs fully on at 4.5V) are easily available.

    Just pick more capable parts.