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Thread: Need assistance with designing a Single input 120VAC and dual output DC converter

  1. #11
    Join Date
    Jun 2003
    Location
    Hawthorne, New York NEC: 2014
    Posts
    3,576
    Using a buck converter rated for 5v, 30 Watts I can power 2 ipads. I want to use a 12v output from a driver and use that as an input for the buck.
    Buck converter?? Most 12v to 5v USB "chargers" are a simple 5v regulator IC. If your 12v supply should dip that is one of the reasons for the regulator, it should still provide 5v with an input well below 12v. If you are that concerned about supplying an iPhone with less than 5v someone can design a supply that will cut off during an under voltage condition. But that's not something that you are going to buy off the shelf.

    If you were able to obtain the design of a Apple iPhone 120VAC charger you will see that there is a lot more going on than simply providing 5vdc. This is why aftermarket chargers or connecting to a USB port take forever to charge the phone- as will your scheme.

    -Hal

  2. #12
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    6,843
    180217-0952 EST

    Sarray:

    Since you are concerned about your iPads, then you need to find out more about the iPad.

    What does the I-V curve look like from 0 to say 6 V for a fully charged, and near fully discharged iPad. From this you can probably determine whether you need protection from abnormal voltage in this range, or back-current feed.

    For protection from higher voltages you may need a fuse, and something like a Transorb. A Transorb is a commercial product that is a specialized Zener diode designed and specified for transient voltage limiting.

    If you can't find authentic information on the iPad and don't want to experiment over a wide voltage range, then test over 4.5 to 5.5 V. Depending upon what this tells you design a circuit that opens the circuit to the iPan for any voltage outside what you determine to be an acceptable range.

    .

  3. #13
    Join Date
    Jun 2003
    Location
    Hawthorne, New York NEC: 2014
    Posts
    3,576
    Quote Originally Posted by gar
    What does the I-V curve look like from 0 to say 6 V for a fully charged, and near fully discharged iPad.
    Well, maybe but maybe not.

    I'm sure the charging operation of the Apple charger and the phone itself is proprietary. I suspect information is exchanged between the phone and charger to provide a fast controlled charging (ie highest current vs temperature vs time). About the only given is that you can charge the phone via a USB cable from a 5vdc source, but even if the source can provide current equal to the Apple charger, the phone won't use it resulting in a much slower charge time.

    I also don't believe that the phone can be damaged by an under voltage.

    -Hal

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