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I Why do some devices work for a short time after unplugged?

  1. Feb 21, 2017 #1
    Hi.
    Some laptop or mobile phone chargers still work for a couple of seconds after being unplugged. I've also seen similar behaviour with the standby lights of monitors, TVs and other devices after they are disconnected from power. Is this due to self-inductance in the transformer? If so: If self-inductance is able to maintain a substantial current for several seconds, how can those transformers operate under normal conditions where the direction of current is supposed to change 100 times per second (at 50 Hz)?

    Or is this just some capacitors discharging?
     
  2. jcsd
  3. Feb 21, 2017 #2

    berkeman

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    This.
     
  4. Feb 21, 2017 #3

    Vanadium 50

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    What makes you think anything except the "on" LED is working? (Particularly in devices without capacitors)
     
  5. Feb 21, 2017 #4

    berkeman

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    For devices that I design, the "On" LED is just powered from the output rail through a resistor.

    I have had multiple times when I've plugged an unpowered power supply brick into a device where the device tried to power up. That's just the output capacitors of the brick holding their charge an unexpectedly long time. :smile:
     
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