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Beginner transformer question

Discussion in 'Electronic Basics' started by Ant_Magma, Feb 26, 2006.

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  1. Ant_Magma

    Ant_Magma Guest

    I'm looking for a transformer that is capable of stepping down 240V
    from the wall outlet to maybe less than 20V depending on the type of
    voltage regulator. My objective is to produce 3.3V from the wall outlet
    to power my ICs.

    1) Most of the times i see 2 same values for the secondary voltage, eg:
    0-9,0-9 (9V). What does it mean? Does it mean i still get 9V output?

    2) If i want to calculate the output current, do i take the power
    rating lets say 3VA and divide with the output voltage, for example 3VA
    / 9V=0.33A?
     
  2. Jamie

    Jamie Guest

    power is power, if the device can only deliver 100 Watts for example,
    that is what you get .
    when you scale down the voltage you simply get higher current at the
    lower voltage which can still work out to the same max watts.
    if you know the wattage of the supply source via the label on the
    unit? then you can calculate the amps you will expect to get .
    Watts/Volts = Amps.
    so if lets say your little step down supply is 100 watt handling and
    you have 9volts, the current should be a little less than 11 amps/.
    i say a little less is because of other factors that come in when using
    something like a xformer. you have losses and efficiency factors.
    that is about as basic as i can get it.
     
  3. Ant_Magma

    Ant_Magma Guest

    But i do not know how much is the power supplied by the power outlet.
    How do i calculate the output current then?
     
  4. Rich Grise

    Rich Grise Guest

    Is the assignment "make a power supply", or is the assignment "these ICs
    need 3.3V @ 500 mA"?

    If all you need is volts, then go here:
    http://www.globalsources.com/gsol/I/AC-DC/p/2000000003844/3000000149681/sm/1000560192.htm
    [mind the word wrap]
    and look at:
    GFP051-A315: 3.3V/1.5A

    They don't show prices, but it can't be as much as you'd spend trying to
    duplicate it.

    If the assignment is "learn how to build a power supply", then any of the
    basics tutorials should help here, or "Art of Electronics", by Horowitz
    and Hill.

    Good Luck!
    Rich
     
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