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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



  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.

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