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Looking for low resistance Analog SPDT

Discussion in 'General Electronics Discussion' started by GCC, Jul 5, 2013.

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  1. GCC

    GCC

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    Jul 5, 2013
    I'm searching for a reliable simple part, maybe someone can help.

    Does anyone know any good SPDT switches that can carry 1A at 3-5V with low power dissipation? I want to be controlling it with a 5V hi-lo signal.

    Thanks!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Any switch that has a rating of 1A or more will suffice.
     
  3. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    This (see bold) is not clear to me. Is it a SPDT Switch or SPDT Relay that you're looking for? Either way there are copious models out there.

    Chris
     
  4. GCC

    GCC

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    Jul 5, 2013
    I'm not sure which is a better approach (switch or relay). Right now I'm looking choosing between a power transistor switch or a relay approach trying to save both money and power dissipation in the circuit. I want to toggle the switch based on whether or not external power (supplied at 5VDC) is available or not.

    I'm leaning towards using transistors for it.. does that seem reasonable?
     
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Yes but with a caveat. Transistors used in switching mode work best when they're switching to the negative rail (0V) of the supply. We call this Low Side Switching. Transistors can switch the positive rail of the supply (High Side Switching) but it requires PNP Transistors or PCHAN MOSFETs, which most of us like to avoid.

    Chris
     
    Last edited: Jul 6, 2013
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    My first thought is that a MOSFET is what you want. These are available with very low ON-resistances - down to 1/1000th of an ohm! They need a DC bias on the gate to turn them on.

    Some MOSFETs (called "logic-level gate" types) can switch heavy currents with a gate bias voltage of 5V or less. Most are only available in SMT (surface-mount technology) packages, but a few are available in THT (through-hole technology) packages. Check out this one:

    http://www.digikey.com/product-detail/en/NDP6020P/NDP6020P-ND/1055922

    This is a P-channel MOSFET, which is easier to drive if you're switching a positive supply rail. You can use N-channel MOSFETs but a gate bias circuit is required. N-channel MOSFETs have lower ON-resistances than P-channel MOSFETs. (The device linked above has an ON-resistance of 0.05 ohms with 4.5V of gate bias.)

    If you want a SPDT switch, you'll need two of these. And you'll need some circuitry to control them.

    What voltage do you want to switch? You need to describe your application in a lot more detail.
     
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