5V Transformerless Power Supply

Discussion in 'General Electronics Chat' started by fnicoli, Jun 26, 2015.

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  1. fnicoli

    Thread Starter New Member

    Apr 8, 2014
    3
    1
    Hey guys!

    Intro
    I'm building a small microcontrolled contraption (a custom timer) that I plan to put inside of the power outlet box.
    Due to the low power requirement of my project and the small amount of space available, I cannot use a transformer.

    What I did
    I designed the thing on the attachment using standard component values -correct me if I'm wrong- in such way that the 2.2k resistor gets a 7v voltage difference between its terminals (just a little bit higher than the 5v I need).
    The diode then cuts off the negative half of the wave and charges the capacitor that acts like a filter. The zener diode brings the voltage of the output to 4.89v, which is a little lower than expected but still not a problem.
    The 1Mohm resistor discharges the capacitor in less than a minute (tau = 10s) and consumes around 5 microamps without external loads on the output.

    supply.png

    What happens
    When I simulate a 5kohm load, Vout drops to 2.44v. Geez! With a 1k resistor, the voltage drops to about 1v!

    WTF
    I'm fully aware that the circuit wasn't designed with any power requirements in mind except the output voltage, however I don't know the reason the circuit is not able to provide 1mA without dropping Vout to 1v.

    PLZ HALP
    What advice could you give? Which design considerations should I have in mind when designing such circuit?
    And why the voltage drop is soooo huge?


    Thank you for the attention.
     
  2. #12

    Expert

    Nov 30, 2010
    16,261
    6,770
    Das ist verboten!
    Sorry, this site forbids that kind of circuit as, "too dangerous".
    It was in the Terms of Service which you agreed to.
    There are no Moderators on duty right now, so I'm taking the responsibility to draw a line around this territory.

    (Please try Electrotechonline)
     
  3. fnicoli

    Thread Starter New Member

    Apr 8, 2014
    3
    1
    Oh, sorry. I really missed that.
    I'm actually only interested in the engineering process and math behind the circuit operation.
    I know it is dangerous but had no clue it was against the forum rules. Sorry for the inconvenience.

    -----
    EDIT
    I'm guessing why this subject is forbiden.
    People generally know not to mess with electricity without knowledge.
     
    #12 likes this.
  4. #12

    Expert

    Nov 30, 2010
    16,261
    6,770
    Thanks for being polite about it. You will find a butt load of good people and good advice here, if you hang around, but this one will get our knuckles rapped by the moderators. ;)
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Have you seen a USB cube? They are 5V and extremely small, and can go to 2.1 A. They are not transformerless. As is I'm afraid I'm shutting this down. The reason it is against the rules is they are dangerous.
     
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