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Transformer less Power Supply

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Suraj143, Sep 18, 2017.

  1. Suraj143

    Suraj143 Active Member

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    I need to make a reliable transformer less power supply to my infrared project.Attached a drawing & needs comments.

    Relay takes 30mA Current.A total current of 40mA-50mA more than enough for me.
     

    Attached Files:

    Last edited: Sep 18, 2017
  2. schmitt trigger

    schmitt trigger Active Member

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    Looks good.
    But...........in transformerless supplies it is always good practice to reduce the total current draw.

    For instance:
    I assume that your relay is 30 mA @ 5V.
    If you change the relay coil to 12V and feed that from the voltage previous to the 7805, then a similar relay will only draw about 12.5 mA.
    You would need an external NPN transistor to drive it, but those are really, really cheap.
     
    • Like Like x 1
  3. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    The 1N4007 could be 1N4001. There is no high voltage on these diodes.
    ---------edit--------
    The voltage is high across the 1M resistor. Many resistors can not take that much voltage. You might need to use 2, 3, or 4 resistors to reduce the voltage each.
     
    Last edited: Sep 19, 2017
  4. dave

    Dave New Member

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  5. Suraj143

    Suraj143 Active Member

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    Hi thanks for the view.

    Regarding the voltage across 1meg...

    (230×1.414) - 30V = ~300V
    V=IR
    300=I × 1000000
    0.3mA = I

    You mean 1/4w resister not enough?
     
  6. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Resistors have a maximum voltage rating, as well as a maximum power dissipation rating...
     

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