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Simple & cheap 'off line' power supply?

Discussion in 'Electronic Design' started by Rolavine, Nov 18, 2004.

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  1. Rolavine

    Rolavine Guest

    I need to make about 24 volts DC (good enough for dc relays) at about 250 ma
    maximum from either 110v or 220v ac input.

    I've found a bunch of circuits online, and quite a few chips.
    I would like to avoid using a switcher because of EMI.
    I think I need too much current for a shunt type approach.
    Does anyone know of any simple SCR based, 'light dimmer' type circuit that can
    be used for an off line supply. I have a PIC onboard that has a battery back
    up, so it could run the SCR? I just looked up sensitive gate SCR's and it
    didn't even seem impractical that I could trigger it through a capcitor?

    Any other advice on a best cheapest approach would be helpful. I've done these
    before for cheap control circuits but have never needed this much current
    before.

    Thanks

    Rocky

    Rocky
     
  2. Active8

    Active8 Guest

    If you mean "divider", 2.5 A through the divider.
    A triac uses both half cycles. Both give EMI in the simplest
    circuits. Hint: thyristor data book.

    I don't like to recommend an offline supply that's not isolated,
    something easily afforded in a switcher - and your batt backup might
    power the controller. Or a PVI opto isolator driving the thyristor,
    I guess.
     
  3. For 250mA, use a transformer.


    Best regards,
    Spehro Pefhany
     
  4. Fred Bloggs

    Fred Bloggs Guest

    You can't beat something made out of junk TV parts- this circuit should
    suit you well:

    View in a fixed-width font such as Courier.
     
  5. Rolavine

    Rolavine Guest

    From: Fred Bloggs
    Great circuit, I think, where did you get it from? It was exactly the kind of
    thing I was thinking about.

    Rocky
     
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