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Need a circuit (220v to 12) low current.

Discussion in 'Electronic Basics' started by ahonda55, Sep 11, 2005.

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  1. ahonda55

    ahonda55 Guest

    Hi great forum :
    i need a circuit to convert the 220v AC to 12v DC , but without coil
    (i have no experience in coils ;)
    i saw a circuit many months ago using a capacitor and some other part
    i can't remeber
    i need this circuit to run a very low current circuits like the NE55
    circuit and about 5 mA relays etc. etc.

    is that possible ?

    ThanKs A lOt :

    regards

    Ahme
     
  2. Sorry to say, coils are almost certainly involved in a reasonable
    solution to this problem. Many small electrical devices are powered
    by small transformer based supplies that hang on the wall receptacle.
    I don't know what country you live in, but I suspect that there is
    some nearby source of such small supply that will provide something
    close to what you need.

    The unregulated ones are all based on something like:
    http://www.electronics-tutorials.com/basics/power-supply.htm

    But some include a linear 3 terminal regulator:
    http://www.hometech.com/power/powersup.html#XA-781RG

    These little wall mounted transformer supplies have been made in such
    numbers that I would be surprised in there are many around you for
    salvage or purchase.
     
  3. ahonda55

    ahonda55 Guest

    Thanx a lot , i live in Egypt , and there is a lot of wall-moun
    transformers here, but i was looking for make a simple circuit lik
    the one i had seen

    i will search for that page and when i find it i will post it here

    Thanx a lot
     
  4. Dan Akers

    Dan Akers Guest

    "i need a circuit to convert the 220v AC to 12v DC , but without coils
    (i have no experience in coils ;)   )
    i saw a circuit many months ago using a capacitor and some other parts i
    can't remeber.
    i need this circuit to run a very low current circuits like the NE555
    circuit and about 5 mA relays etc. etc.
    is that possible?"
    ____________________________________
    Re;
    Yes it is possible to use the capacitor as a zero power voltage dropping
    device. A 0.2uF cap in series with a .5A fuse and two back to back 1W,
    18V zeners will provide an 18.7V (or so) clipped AC waveform across the
    zeners. This can be fed into a full wave bridge and then flitered by a
    capacitor of 470uF or so and then you could use a 7812 (or other fixed)
    three terminal regulator to get the requisite 12V.
    Just keep in mind that the circuitry will not be isolated from the main
    potential and will present a shock hazard.

    -Dan Akers
     
  5. ahonda55

    ahonda55 Guest

  6. ehsjr

    ehsjr Guest

    You said you want a simple circuit. Please follow
    John's advice - use a wall transformer. It *IS*
    simple - simpler than wiring up a capacitor and a line cord.

    If you want to build the DC supply, use a wall transformer
    that lowers the voltage from 220 to ~12 volts AC, a capacitor,
    bridge rectifier and a 3 terminal voltage regulator chip. That
    will be MUCH safer for you, and will do what you want. The
    circuit on the link you posted will not drive a relay.


    LM7812
    ---------
    +-----------+--- |in out|--- Vout +12
    | | | Gnd |
    --------- ------ [C1] ---------
    | Wall | | + | | |
    ---| Trans- |-------|~ BR ~|---+ +----------+-------- Gnd
    ---| former |---+ | - | | |
    |220 12| | ------ | |
    -------- | | | |
    | Gnd | Gnd
    | |
    +--------------+


    BR = bridge rectifier
    C1 = 2200 Uf 25 V
    Use a LM7812 3 terminal voltage regulator in a TO220 package

    Ed
     
  7. ahonda55

    ahonda55 Guest

    Ok friends , i will get you advice

    Thank you very much
     
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