Berkeley CSUA MOTD:Entry 34170
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2017/12/16 [General] UID:1000 Activity:popular
12/16   

2004/10/16-18 [Science/Electric] UID:34170 Activity:high
10/16   Has anyone had AC power adapters that are slightly warm even when
        it's not connected to the device that uses it? Obviously, this means
        it must be consuming energy even when it's not transforming anything,
        but why should it be?
        \_ Every AC adapter generates some heat...some much more than others.
           Inside, you have active devices that are constantly working to
           keep the output voltage constant.  Many adapters use LDOs (Low
           Drop-Out) regulators which drop about 1.2V.  Any device that
           has a voltage drop is consuming power, which becomes heat...
           \_ But he asked about when it's not being used.
            \_ Same answer.  I never said anything about a device being
               plugged in.  A regulator will still consume power even if
               nothing is plugged into the output.  It still must regulate
               the output voltage, even if no current is flowing out the
               connector of the power brick.  Internally, you have leaky
               capacitors across the output, and the feedback circuit to
               the regulator is usually done with a resistors, which always
               have current flowing through them.  So, same answer.
        \_ The simple answer is that even when not in use they are an open
           circuit and will drain power, though less than if they are in use.
           You could design them to sense if there's a load and only open the
           circuit then, but that would add to the cost and complexity
           (although in the long term save you money I'm sure).
           \_ you've got your opens and your closes backwards.
2017/12/16 [General] UID:1000 Activity:popular
12/16   

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