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230ac to 5vdc

Discussion in 'General Electronics Discussion' started by gregz0012, May 19, 2013.

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  1. gregz0012

    gregz0012

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    May 19, 2013
    I have put together a circuit to take mains 230vac down to 5vdc for use in phone chargers, USB hubs etc.

    I plan to replace the LT1085-12 and LT1084-5 with cheaper versions, such as BA17805T etc. I'm using the 12vdc regulator to smooth the current before using the second regulator to reduce to 5vdc. However, is the second one necessary (ltspice shows a fairly wavy voltage output without the second one)?

    I'm fairly new to electronics, so may have missed something.
     

    Attached Files:

  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    You don't need 2 regulators. What you need is a larger capacitor where C1 is. Something like 1000uF.

    Bob
     
  3. gregz0012

    gregz0012

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    May 19, 2013
    Thanks Bob, I've removed the 12v regulator and the capacitor in between the v regs, also increased C1 to 4700uF which seems to give me a stable 5vdc all the way up to 5 amps.

    In LTSpice I have to add R1 to get the simulation to run, is R1 really necessary?
     
  4. davenn

    davenn Moderator

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    R1 is in the primary, no it shouldnt be there

    Dave
     
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    That xfmr indicates Pri= 50uH, Sec: 400uH. I don't think so and may be why LT Spice is upchucking without the 1Ω in the primary. The input current will be in the ozone without it.

    Chris
     
  6. gregz0012

    gregz0012

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    May 19, 2013
    Your right, I couldn't find the values from my transformer so plugged in a set of numbers that get me the desired voltage.
     
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Your Transformer model appears to be modeled as Coupled Inductors. Does LT Spice provide a Transformer model also? Transformer models are modeled in terms of turns ratio,coupling (k) coefficient, Rprim, Rsec.

    Chris
     

    Attached Files:

  8. gregz0012

    gregz0012

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    May 19, 2013
    Unfortunatly not (see docs)
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Put an Ammeter in line with the primary. With inductance that low I expect to see excessively high current ... especially if you shunt that 1 Ohm resistor.

    Chris
     
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