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Laptop transformer size

  1. Sep 18, 2012 #1
    Why laptops transformer size varies so much?
    Also, the little cylinder right next to the cable connector to the laptop is there to avoid that the laptop works as an antenna? How does that work?
    Thank you
  2. jcsd
  3. Sep 18, 2012 #2


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    Hi Charles

    Most laptop PSU's these days are switchmode type. There isnt too much variation in physical size. any variation in size is mainly related to the variation in current capabilities of the supply. a 5A or so supply is going to need a physically larger transformer than one that only requires 3 or 4 Amps.

    That little cylinder is an encapsulated ferrite core that the DC supply cable passes through before getting to the laptop.
    It has 2 purposes ...
    1) to filter any hi frequency generated by the SMPS from getting into the electronics of the laptop and causing instability problems
    2) it also has the reverse filtering effect. the microprocessor circuitry etc of the laptop produces lots of RF at many frequencies. That ferrite core filters much of that out so that the DC power cable doesnt act like an antenna and radiate those signals

  4. Sep 18, 2012 #3
    Thank you for your answer. But actually, and just as an example my Toshiba Qosmio x770, has a transformer twice as big and tree times heavier that my ASUS… none of them is more than 2 years old.
  5. Sep 18, 2012 #4


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    What wattage does each output? How big are the laptops?
  6. Sep 19, 2012 #5


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    yeah that was going to be my next question

    what is the voltage and current ratings of the large one compared to the small one ?

    I still stand by what I stated its all to do with the current the unit needs to supply that determines its overall size

  7. Sep 19, 2012 #6
    I understood your explanation, I was just comenting the diference in sized because you wrote - "There isnt too much variation in physical size.".
    Thank you again
  8. Sep 19, 2012 #7

    jim hardy

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    @ OP:

    each is labelled with its output volts and amps. Look carefully at the small print on nametag.

    If you read electronic design magazines there is a continual push to pack more power into smaller volume
    so your observation is right - there is a LOT of variation even among swichers.

    it comes down to the skill of the design and manufacturing teams, can they find small parts and can they arrange to get rid of the waste heat
    there have been plenty of overheating failures from "design oops'es", believe me.
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