Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Input and output voltages and amps on my laptop's charger

  1. Apr 9, 2016 #1
    The wire on the charger that came with my laptop eventually frayed, and I had to buy a new charger for my laptop. Both the new and old chargers for my laptop plug into a standard wall outlet. On the new charger, it says the following: " Input: 100-240V ~ 1.5A 50-60Hz Output: 19V --3.42A 65W MAX. "

    I assume that the V stands for voltage, and the A stands for amps. But why is there a different voltage for input and output? What is the meaning of input and output? Why is there a different amperage for input and output?
  2. jcsd
  3. Apr 9, 2016 #2


    User Avatar
    Gold Member

    Google "electrical transformers" (your charger is a transformer)
  4. Apr 10, 2016 #3


    User Avatar

    Staff: Mentor

    Your laptop needs 19 volts to operate, but your wall socket provides 120 volts. The charger is a transformer that steps down the input voltage so it doesn't damage your laptop. It then outputs this stepped down voltage to your laptop.

    The amperage is different because of the way the electronics work. To operate, your laptop needs electrical power. Power is given by the equation P=IV, or power equals current times voltage. This means that you can provide the same amount of power with different currents and voltage as long as their product is the same. Your laptop charger only takes in up to 1.5 amps, but it can supply up to 3.41 amps to the laptop at a reduced voltage. Note that the voltage required by the laptop remains the same during use, but the amount of current drawn by the laptop will change as you use it. If you're doing lots of processor/graphics intensive stuff you will draw more amps than if you just sit there at the desktop.
  5. Apr 10, 2016 #4
    You can feel when the laptop draws more power by touching the transformer.
    As you use more power (which is equivalent to more current) the transformer will heat up.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted