DIfference between usb 5V and dc adapter 5v.

Discussion in 'General Electronics Chat' started by nepdeep, Oct 24, 2012.

  1. nepdeep

    Thread Starter Member

    Sep 14, 2011
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    I have noticed that the phone charges more faster with Adapter ratehre than USB from PC. measured the voltage and both of them from PC and adappter are same...why is the charging time difference then. As far as i think...The current is same as the load is the phone itself in both case ..so like kind of constant load...!! Any ideas ladies and gentlemen!
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    USB ports are current limited.
     
  3. JMac3108

    Active Member

    Aug 16, 2010
    349
    66
    You assume the current is the same, but it probably isn't. I just designed a device that charges a battery and I reduce the charge current when USB is the power source so as not to exceed the 500mA USB limit, and increase the charge current when an external adapter is present.
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
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    Apple probably recognizes it´s own adaptors, so the phone can tell that it can use more current.
     
  5. colinb

    Active Member

    Jun 15, 2011
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    There is often a special pull-up resistor in those high-current USB chargers for phones and other mobile devices, the value of which signals the current capability of the charger (either 1 A or 1.5 A, usually).
     
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