Simple Power Supply - 5VDC from 240Vac?

Discussion in 'General Electronics Chat' started by axeman22, Jul 7, 2009.

  1. axeman22

    Thread Starter Active Member

    Jun 8, 2009
    53
    0
    I'm looking to make a TV timer for the kids.. yes, my kids put the TV on then just walk away.. drives me mad! .. so this way they will need to press a button every X period of time, probably 15 minutes.

    I want to keep it as cheap and simple(and safe) as I can.. take a look at the diagram.. what is the simplest and chepest way to take 240VAC down to a usable 5Vdc for 555 timers, PICAXE chip etc.. without needing a transformer and the big guns ..???

    I was thinking, Diode Bridge, some resistors, voltage Reg like LM317(?) etc.. few Caps.. not much more

    appreciate all thoughts/input! .. current is so low.. so thinking/hoping I should be able to not need a transformer.
     
  2. millwood

    Guest

    the simplest would be to use a capacitor to lower the ac before rectification.

    however, it carries significant risk as well, and if your relay draws tons of current, it may not work.

    the cheapest would be to get an ac power supply from wal-mart and be done with it.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Only a transformer will provide isolation (and thus safety) from mains power.

    You can buy "wall warts" (plug-in unregulated DC power supplies) just about anywhere, or use one from a discarded appliance.
     
  4. Externet

    AAC Fanatic!

    Nov 29, 2005
    759
    57
    That button will be attached to the TV, right? Tap the 5V from the inside the TV itself to supply your timing circuit. That 5V will be present only when the TV is on; and the timer circuit can trigger the internal TV power-off button circuitry. Only a button will show on the side/back of the TV cabinet.
     
    Last edited: Jul 7, 2009
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