small transformers

Discussion in 'General Electronics Chat' started by Zanac-X, Sep 17, 2012.

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  1. Zanac-X

    Thread Starter Member

    Dec 23, 2011
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    hey guys :)

    if you open up a mobile battery charger you should see a circuit that has a small transformer in it and i was wundering is that really a small transformer and if it is then why do we use large once.......is it the current that determine the size ?


    and how do you know the ratio and voltage capacity of the coils of the transformer when its small because there is no specifications on them ?

    thanks very much
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    The large transformer you see in a linear power supply serves a particular purpose - to transform high voltage/low current AC at 60Hz to low voltage/high current AC.

    What you see in a battery/lap top charger might not be a transformer.
    It could be an inductor.
    A switching power supply runs at a much higher frequency. Hence the inductance or transformer required is smaller.
     
    Last edited: Sep 17, 2012
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    If the charger is a line to low-voltage DC power supply it is indeed a transformer. Otherwise it would not be isolated.

    Ken
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Because the small one is a SWITCHED MODE PSU , and doesn't need to be big in size as its "chopping" the mains supply, and not dropping it down like a conventional 50/60Hz transformer.
     
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  5. Sensacell

    Well-Known Member

    Jun 19, 2012
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    It probably IS a transformer.

    Here is the key- low frequency (mains) = BIG FAT HEAVY power transformer

    High frequency (100's of khz) = SMALL power transformer.

    A switching power supply works by converting the mains voltage into a very high frequency signal that makes efficient use of low inductance small magnetics.

    The transformer works just like a standard mains transformer providing isolation and voltage step-down, only it operates at a high frequency, not 50/60 Hz.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    The size of a transformer is determined by its current rating (which affects wire size), its operating voltage, and its frequency of operation. The frequency and voltage determines the required transformer inductance (reactance) required to keep the idle (magnetizing) current at a reasonably small level. For a given reactance, lower frequencies require a higher inductance, thus more turns and a larger core.
     
  7. szhighstar

    New Member

    Jun 26, 2012
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    I guess it is power inductor, is not transformer.
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Why??

    Ken
     
  9. richardlionheart

    New Member

    Sep 7, 2015
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  10. WBahn

    Moderator

    Mar 31, 2012
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    Chances are that none of the participants are still interested in responses to a thread that was last active just shy of three years ago.
     
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