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How-To/Which passive switch with lowest possible control power

Discussion in 'Electronic Design' started by [email protected], Jun 24, 2007.

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  1. Guest


    I need to create a passive switch (which means it must not require to
    be powered) whose control power is AS LOW AS POSSIBLE (ideally below
    the milli Watt range) and the supported power on the secondary circuit
    in the multiple milli Watt range.
    Which components should I use ? An analog switch (which one), a single
    transistor (which one), etc. ?
    Does anyone have a sample circuit ? Any link suggestion ?
    The most important feature is that the control power is as low as
    possible (sorry I say it again).

    Thanks in advance
  2. MooseFET

    MooseFET Guest

    Huh ???? Do you mean that it must only draw power from the control

    Take a look at power MOSFETs. For DC on the gate, they draw nearly no
  3. colin

    colin Guest

    A latching relay doesnt require power at all,
    just a small amount of energy to change its state.

    just depends how frequenctly you switch it as to wether this is low enough

    or maybe this wasnt what you meant when it must not required to be powered.
    a mosfet switch requires power to control it, albeit minuscule.

    Colin =^.^=
  4. Guest

    Thanks for the answers

    a latching relay could be a solution (teoretically the ideal one) if
    there is one that can change state with very little power (ideally
    much less than 1 mW).

    About the solution with the MOSFET, what are the ones with the lowest
    DC on the gate (vendor/model) ?

    Thanks for any additional tip
  5. colin

    colin Guest

    a latching relay isnt specified by power, but by energy,
    many battery powered devices use them,
    you would need to store up sufficient charge in a moderate size capacitor.
    you can get 3v mosfet switches.

    not sure of models, digikey probably list both these devices.

    Colin =^.^=
  6. Guest

    Hi Colin

    thanks for the answer.
    I looked a little around for the MOSFET solution, and I found that the
    most "sensible" ones requires on the gate-source still 3 volts and
    consume 2 ampere (???) DC to saturate. This makes still 6 watt control
    power to switch my passive switch. Isn't there a more "sensible" way
    to reach my scope without using an active circuit ?
    Sorry for my "beginner" questions, but my understanding of electronic
    is quite basic.

  7. colin

    colin Guest

    they dont require 2A to control,
    that probably refers to the maximum current it can switch.
    typicaly gate resistance will be megaohms,
    so current will be microamps or less.

    Colin =^.^=
  8. MooseFET

    MooseFET Guest

    TN0604 or TN2501 would need very little energy to switch.
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