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How to turn On/Off a +5vcc power?

Discussion in 'Hobby Electronics' started by Johan Harold, Aug 29, 2005.

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  1. Johan Harold

    Johan Harold Guest

    I have a set of sensors and actuators all operating at +5v and draw 10mA to
    680mA current.
    My microcontroller will stwitch these units ON or OFF in various
    configuration. My microcontroller has enough output port to drive switching
    circuits.

    How can I switch these unit ON/OFF without using mechanical relay?
    What is the electronic equivalent of relay ? (May be FET/MOSFET ? How to
    drive them?)
     
  2. Wing Wong

    Wing Wong Guest

    MOSFETs are good start. Try something like a MTP2955, IIRC it has quite a
    low on resistance only about 0.2 ohms and a threshold voltage of about 3
    volts. Its the cheapest MOSFET I can think of. This is device is a
    PChannel device so let me see... tie the source to the 5V, the drain to the
    Vcc of the things you want to drive and as for the gate, attaching it to the
    output pin of you MC you give you what you want. Driving the line high should
    turn it off and driving it low should turn the mosfet on. Depending on the
    configuration of your MC, you may need pullup a pullup resistor at the
    output pin of the MC.

    I think my advice is correct, but don't take my word on it. Feel free to
    get a second or third opinion.
     
  3. dmm

    dmm Guest

    Check out Fairchild's FDG312P. Rds(on) = 0.18ohms @ Vgs = -4.5V, Vdss max = -20V, Id = -1.2A
    and it's in a SC70-6 package. Sneeze and its gone.. :cool:
     
  4. On Monday, in article
    <>
    Or even Fairchild FDV range logic switching FETs in SOT-23 packages

    Rds Id Id (pulsed)
    FDV304P 1.1R 460mA 1.5A (4.5V Vds)
    FDV302P 10R 120mA 500mA (4.5V Vds)
    FDV301N 4R 220mA 500mA (4.5V Vds)
    FDV303N 0.45R 680mA 2A (4.5V Vds)

    Gate switching < 1.5V so ideal for low load switching in ONE device.
    I tend to use FDV304P and FDV303N for lower Rds and higher Id

    Available in small quantities Digikey, Farnell......
     
  5. The others have responded regarding solid state switches (MOSFETs would
    be my preference, too, though a ULN2003 array would take up less space
    if you need more than one or two), but to add to the confusion: is there
    a reason to shy away from relays? If only 680mA you could probably get
    away with smaller reed relays. You can't hear them, they last for a lot
    of switchings, and they don't need heat sinks. One thing, though, is
    that you can't always drive a bunch of them at the same time from your
    MCU ports. One at a time is usually okay, but of course, check the specs
    to be sure.

    -- Gordon
     
  6. Yes you can use a logic-level MOSFET (p-channel for switching +5V or
    n-channel for switching the ground). There are some nice dual
    low-Rds(on) ones in small 8-pin SMT packages.

    Take care with bypass capacitors on the switched side. These parts are
    so low resistance that if you switch them quickly the bypass caps on
    the switched side can put a glitch on your unswitched power supply.



    Best regards,
    Spehro Pefhany
     
  7. What are the sensors and actuators? Can you get away with a cheap
    trasistor?
     
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