Latching switch for AC

Discussion in 'General Electronics Chat' started by kiranr, Oct 26, 2010.

  1. kiranr

    Thread Starter Member

    May 1, 2009
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    I'm looking for a latching switch which can be triggered by 5V DC and which can switch 230v AC.

    My basic need is that the device will turn on one pulse and will remain on until an off pulse is given.

    I looked into triacs but could not exactly figure out how to achieve the latching. I'm planning to drive household appliances like light and fan.

    I originally thought of latching relays but couldn't find one in ernakulam. Which would be better for home automation?

    Could someone point me in the right direction.
     
  2. kiranr

    Thread Starter Member

    May 1, 2009
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    nobody????
     
  3. zgozvrm

    Member

    Oct 24, 2009
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  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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  5. SgtWookie

    Expert

    Jul 17, 2007
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    If the 230v being switched is L1 and L2 (two "hot" leads) then both must be switched; otherwise the appliance or device will still be connected to the mains when just L1 or L2 are interrupted.

    If there is just L1 (hot) and Neutral, then you can simply switch L1.
     
  6. zgozvrm

    Member

    Oct 24, 2009
    115
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    Good point. I replied a bit too quickly. Should probably actually use a 3PDT relay (or only 3 of the 4 contacts of a 4PDT relay).
     
  7. kiranr

    Thread Starter Member

    May 1, 2009
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    Latching relays were my first considerations. (I'm using single phase.) But with relays there is the switching sound and as this is for appliance control at home, i was trying to get rid of the noise and improve durability. Plus, I wanted to learn about solid state switching.

    Of course, if not viable i understand that relays are the way to go.

    Thank you for your replies.
     
  8. engineer2010

    New Member

    Oct 31, 2010
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    You can use high voltage MOSFETs. They are easier to control than a TRIAC; however, you will need to use two in series because you are switching an AC signal, and a MOSFET has an intrinsic (built-in) diode that will conduct for one half of the AC cycle.

    You can design a circuit similar to Kermit's where the output powers the gates of the FETs, or latching can be built from some digital logic, if you have the space for ICs.
     
  9. kiranr

    Thread Starter Member

    May 1, 2009
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    thank you engineer2010,
    Will take a look at that.
     
  10. zgozvrm

    Member

    Oct 24, 2009
    115
    2
    You might look into opto-isolated output modules. I use input and output modules from Opto-22 (see http://www.opto22.com/). The also have solid state output modules for higher power switching.

    As for latching, you would do that in the control logic.
     
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