Laptop battery/power supply question

Discussion in 'General Electronics Chat' started by electronewb, Apr 13, 2014.

  1. electronewb

    Thread Starter Member

    Apr 24, 2012
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    What makes the voltage going only one way in a laptop? In other words what makes the voltage not going from the battery back to the power supply?

    Reason why I ask is a few days ago I plugged in my laptop power supply in my laptop and it wasn't even plugged in into and AC wall outlet and I saw some arching. The DC in connector seems fine no damage but I was wondering why it happened.
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Diode setup as Blocking Diode. It allows current to flow only in one direction.
     
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  3. wayneh

    Expert

    Sep 9, 2010
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    Or a MOSFET that is turned off to prevent current flow, i.e. an "active" blocking diode instead of a passive one.
     
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  4. electronewb

    Thread Starter Member

    Apr 24, 2012
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    Where does diodes would physically be? What can I look for for a schematic online? Also what would happen if the current would get fed back to the power supply?
     
  5. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Probably in the ac adapter, a.k.a. black brick.
     
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  6. Evil Lurker

    Member

    Aug 25, 2011
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    Generally lithium ion batteries in laptops have their own PCB responsible for keeping track of the charging. After a PSU is disconnected the plug might become charged at the voltage of the battery output. In this case it is possible for a reverse charge to get carried back into the PSU as it's output filter caps on the secondary side would get charged up along with some of the PSU regulatory circuitry and possibly an LED.
     
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  7. electronewb

    Thread Starter Member

    Apr 24, 2012
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    Trying to find an actual schematic for a laptop battery charger/PSU but no luck Lots of usage of a blocking diode for solar panels so the voltage doesn't stray back to the panels and draining the battery
     
  8. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Voltage is a field, it does not need blocking diode.
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Laptop power supplies usually have a flyback circuit topology. The output section is the transformer secondary, a rectifier diode, and some filter stuff. The output rectifier is perfectly positioned to act as a reverse blocking diode, preventing the power supply output circuit from discharging the battery when the charger is connected to the laptop but unplugged from the wall.

    Separate from this, the laptop battery management system might have its own protection circuits.

    The arc you saw probably was either:

    a) residual charge on the power supply filter capacitors discharging into the laptop's input capacitors. First contact between the two connectors is briefly intermittant like contact bounce in a switch. The arc happens with the initial contact breaks.

    or b) static electricity.

    ak
     
    Last edited: Apr 14, 2014
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  10. electronewb

    Thread Starter Member

    Apr 24, 2012
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    Great thanks for all the replies now it's much clearer. Another question some laptop power supplies have 4 or 5 pins I assume they have different voltage on each pins? What's the main reason for that?
     
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