Understanding Laptop Power Supplies & Inventers

Discussion in 'General Electronics Chat' started by Management, Nov 26, 2012.

  1. Management

    Thread Starter Active Member

    Sep 18, 2007
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    Hi Everyone,

    I would like to inquire about laptops and the electronics in them.

    I know laptops can be charged while they are in use but what enables this to happen?

    I know there is a AC to DC rectifier in the power cord and then I know there is some DC to DC power supplies (and regulators) on the motherboard. But,

    what controls the fact that I can charge the battery (especially while it's dead) and use the laptop so seamlessly? I figured the laptop as a whole is drawing more power from the mains to make this happen.

    what allows for the battery to die or be disconnected without experiencing any severe interruption in power when the AC supply is connected?

    Looking for the technical details on what is enabling this to be possible. Thanks!
     
    Last edited: Nov 26, 2012
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Basically you have two diodes, one from from adaptor going to the notebook supplies, and another going from the battery to the notebook supplies. When you have either a battery or adaptor connected, the notebook lives.

    The actual circuitry is much more comlicated, but the basic idea stays.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    Don't forget the charging circuit going from the adapter to the battery.
     
  4. ramancini8

    Member

    Jul 18, 2012
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    The laptop has memory that doesn't need power all the time, so it can be turned off and then on with the memory intact.
     
  5. tshuck

    Well-Known Member

    Oct 18, 2012
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    Yes.... yes it does.. this is called ROM... your point?
     
  6. Management

    Thread Starter Active Member

    Sep 18, 2007
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    Can you elaborate? I don't understand how it fits in.
     
  7. tshuck

    Well-Known Member

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    I wanted to point out that AC to DC uses a rectifier, DC to AC uses an inverter...
     
  8. Management

    Thread Starter Active Member

    Sep 18, 2007
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    Can everyone elaborate in some more detail?

    This assumes only one is connected at a time. But how do they work together to charge and supply power to the laptop? Does the battery supply power while the AC mains charges the battery? Or does the battery get charged and remains unused while the AC adapter is disconnected? I assume the latter but how? What controls this, diodes?

    I think this doesn't happen but is it possible (practical?) to supply power to the laptop from both sources when not enough power is available from the AC plug (supply)?
     
  9. Management

    Thread Starter Active Member

    Sep 18, 2007
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    Thanks! I actually didn't notice I did wrote that. A little brain fart on my end.

    Whats more expensive ... a rectifier or inverter? Roughly speaking in terms of complication.
     
  10. tshuck

    Well-Known Member

    Oct 18, 2012
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    Inverter by a lot.... A rectifier can be built with a single diode(pretty poor quality, but a rectifier nonetheless..)
     
  11. Management

    Thread Starter Active Member

    Sep 18, 2007
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    What about relative to a DC-DC converter?
     
  12. tshuck

    Well-Known Member

    Oct 18, 2012
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    meaning cost of DC-DC converter vs. a DC to AC inverter? it depends on the topology used in each....
     
  13. Management

    Thread Starter Active Member

    Sep 18, 2007
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    I understand that but I'm just trying to understand roughly if one is known to be cheaper or not lumped sum of various factors (of which I don't know hehe)
     
  14. toffee_pie

    Active Member

    Oct 31, 2009
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    why does a laptop need an inverter?

    the power supply is a AC-DC regulator, Switch mode supply.

    all the laptop wants is DC. whether from the Battery, regulated by a BMS or from the brick supply.
     
  15. Management

    Thread Starter Active Member

    Sep 18, 2007
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    No offense but if your going to contribute please read the entire thread.

    No one is suggesting that laptops need inverters or using inverters inside a laptop.
     
  16. crutschow

    Expert

    Mar 14, 2008
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    Many modern AC to DC converters also use a switching inverter for smaller size (due to much reduced transformer size) and better efficiency.
     
  17. Veracohr

    Well-Known Member

    Jan 3, 2011
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    FYI, not all laptops will work without a battery. My Macbook Pro has to have the battery in, even if the supply is connected.
     
  18. toffee_pie

    Active Member

    Oct 31, 2009
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    well thats apple for you...

    its generally good practice to NOT have a battery when its not used, since the heat will do li-ion cells more harm than good
     
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