Power transformers - AC to DC or DC to DC

Discussion in 'General Electronics Chat' started by RogueRose, Sep 25, 2016.

  1. RogueRose

    Thread Starter Member

    Oct 10, 2014
    189
    4
    I am wondering if a transformer like those used in microwaves can be used from a DC source instead of an AC source. Also if DC is desired, is there any reason that the bridge rectifier can't be in front of the transformer? Is there any benefit of rectifying before or after the transformer?
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,348
    Hello,

    Transformers do not work with DC, thats why the rectifier is used after the transfromer.
    In SMPS powersupplies there is a rectifier at the entrance of the powersupply, but the DC that is created is switched very fast so a high frequency transformer can be used, wich is much smaller as a conventional transformer.
    Have a look at the attached PDF on how a powersupply is designed.

    Bertus
     
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  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,555
    2,375
    No you cannot use DC on a normal AC designed transformer.
    The only one that comes close is a synchronous transformer that was often used on car radio supplies, where the 12vdc primary was alternated in synchronous with the secondary windings producing a square wave supply that was then rectified. Achieved with a synchronous vibrator.
    But still AC.
    Max.
     
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  4. Rishi Kumar

    New Member

    Sep 25, 2016
    1
    1
    Yes...transformer can be used on DC if it is switched very fast as it is used in smps power supply. Power supply is first rectified and then switched very fast..also there is a need of high frequency transformer having small size and thus saving space..
     
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  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,555
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    The OP mentions a micro wave oven which has a low freq transformer, the SMPS uses a HF/Ferrite core in order to switch pulsating DC.
    Max.
     
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  6. recklessrog

    Member

    May 23, 2013
    338
    102
    Methinks the OP won't live very long if he starts playing around with microwave oven transformers with no knowledge of what he is doing.

    Desist before you die!
     
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  7. DickCappels

    Moderator

    Aug 21, 2008
    2,659
    632
    Voltage is developed on a transformer's secondary by changing current in the primary. If the current in the primary is constant, as it would be if soon after DC were applied to the primary, there would be no voltage on the secondary except for a brief pulse when the DC source is attached. Post #4 expands on that concept.
     
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