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Latching Relay

Discussion in 'Electronic Design' started by Sparkie, Jun 17, 2006.

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  1. Sparkie

    Sparkie Guest

    I am putting together a project which is designed around low power DC
    (battery driven), and that ultimately results in a high (+5v) or low
    (0v/ground) - a simple change of state to pin out of IC. I have good
    control over this output, and can provide assertion high or low, or
    indeed momentary.

    I intend to then couple this output through a darlington transistor
    pair to provide the necessary current for a relay to then switch mains
    power and operate a mains powered device (eg. a light bulb).

    The problem I have is:
    As the project is battery driven, I MUST be as frugal as possible with
    current drain. I cannot afford any power drain from the battery when
    the relay is in operation and the mains powered device is on.

    What I have considered:
    Latching relay - I think these work by providing a brief trigger to
    energise the coil, the n/o contact is somehow strapped to the load
    side, which then latches the relay on after trigger. Reset would
    require a break in the coil leg to ground/0v. Have I understood this
    correctly? Will there be no further drain from battery after initial

    This initially appear the answer, but as my output is from 1 IC pin
    only (high, low or blip), I am left wondering how to design my cct to
    trigger and re-set the relay?

    Magnetic latching relay - this looks like a strong possibility. I could
    set my output to momentary, then each time pin assertion, the relay is
    triggered and toggled on or off. I believe because these relay on
    magnets, that they do not use or require current to maintain state?

    I don't understand the above working designs / options of these relays
    enough to be confident within my design, could someone help me with my
    understanding and perhaps make comment to my original project
    requirement (ie. battery control, switch on/off of mains power, no
    battery draw when coil/switch is energised).

    MANY thanks,

  2. There are two versions: Dual coil and single coil-dual polarity, both
    retain the last state by magnetic latching in position last ordered.
    Don't know what external device you want to control but after activation
    you can pack your cirquit and take it home and the relay will still
    activate the external device, so some "zeroing" action should be
    implemented on initial power on of the cirquit.
    You are mentioning the current of your battery so, if I would have to
    design such would do something like:
    two separate 5v relays capable of carrying on their contacts the
    currents AND voltages of the main line contactor. One normally open and
    one normally closed. Line contactors usually sport additional contacts
    that can perform the self holding function. So your N/O relay acts as a
    push button to supply line to main coil, the coil enters self holding
    condition and the relay can relax. The other side of the main coil is
    connected to the N/C relay and activating it stops the whole mess.
    So the relay acivations are temporary, when needed.
    The rest is just "logic" left as an excersise for you.

    Happy hunting

    Slack user from Ulladulla.
  3. Stanislaw Flatto wrote:

    Long time since I used magnetic latches relays and I don't recall if
    such exist for 5v range. The ones in my work were the 28v style, and
    needed proper push to change states.
    At least they don't use current when left alone.

    Good luck

    Slack user from Ulladulla
  4. John Fields

    John Fields Guest

  5. John Fields wrote:

    It is now, we did not have such luxury then, it was a a library of
    manufacturers catalogs (tons of it) and a large collection of
    Mil-Speck visual tapes to be read on magnifying screen.
    Somehow we survived it.

    Have fun

    Slack user from Ulladulla.
  6. kell

    kell Guest

    You may wish to consider an alternating relay, which latches
    Each momentary actuation of the coil toggles the relay contacts and
    locks them in the opposite position.
  7. Fred Bloggs

    Fred Bloggs Guest

    A typical datasheet is here: Web Data/G6J-Y Series.pdf
    This is a single coil version, see pdf page 7 for pinout on G6JU
    latching version which indicates coil current into pin 1 and out pin 8
    is "S" for Set, and current into pin 8 and out pin 1 is "R" for Reset,
    the diagrams show the configuration of pins 2-7 in the Reset state,
    presumably, since this is the default factory setting at shipment.
    According to the datasheet, the coil requires an approximately 20mA
    pulse of duration 10ms maximum to guarantee state change at 5V. The most
    uncomplicated way to drive this particular relay with your circuit
    arrangement is to use a series capacitor like so:
    View in a fixed-width font such as Courier.
  8. ian field

    ian field Guest


    IIRC - that's a carpenter relay.
  9. ian field

    ian field Guest

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