NO switch with MOSFET/JFET, Vs=3V, no neg V

Discussion in 'General Electronics Chat' started by hants91, Jul 20, 2011.

  1. hants91

    Thread Starter New Member

    Jul 20, 2011
    1
    0
    Hi, I am new to the forum and looking for some help. I have a circuit which I want to power up when a switch (operated by mechanically) is in Open state. I do not want to used relay.

    State 1: Switch Open - Circuit Power ON
    State 2: Switch Closed - Circuit Power Off

    I considered P-channel MOSFET IRML5103, when the Gate is grounded State 1 activated. But for State 2, I need neg. supply at Gate which I do not have.

    P-N-P transistor can do the job. But it have 0.7 voltage drop which is not acceptable as the unit run by 3V battery and the circuit can run upto 2.2 V.

    I appreciate your suggestions.

    Thanks
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    I have moved your post to the general chat area.

    Can you post a schematic of the intended circuit?

    Bertus
     
  3. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    You do not necessarily need a negative supply for the PMOS. If the PMOS is on the high side of the load, then pulling the gate low will turn it on; letting it float to the drain voltage will turn it off. Ensure Vgs never exceeds +/-20V though; you might use a zener and series resistor for this.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You didn't state what your loads' current requirement is.

    Here's one way you might do it with a couple of PNP transistors and some resistors:

    [​IMG]

    The resistors were calculated for a 3mA load, and Q2 as having a gain of 70.
     
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