Small USB Cellphone Charger - A little help is needed.

Discussion in 'General Electronics Chat' started by Guest3123, Oct 28, 2014.

  1. Guest3123

    Thread Starter Member

    Oct 28, 2014
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    Hi, I'm new here, you can call me Guest, or just Roy. Doesn't really matter.

    So this is what I would like to make.

    Circuit Diagram is as follows.
    IMG00000001 2014.10.28 11.00.57 PM.jpg

    So that's what it looks like.

    I was searching Mouser for quite some time, and learned about LDO Voltage Regulators. But this 511-LF50ABV-DG "VLDO Voltage Regulator. It's pretty sweet it seems.

    That's the Products Main Page, and THIS is the data sheet.

    IMG00000001 2014.10.28 09.59.40 PM.jpg

    It seems MUCH better than a LM7805.

    So.. What do you think? Is it doable?

    Also, I'd like some help understanding some of the data on the data sheet.

    For instance.. What does Output bypass capacitance (C0) mean? is that the type of Capacitor I need on the output on this? 10uF ?

    I also would like to ask.. What is the "Efficiency %" of this little guy? I've seen some other LDO Voltage Regulator IC's and they usually specify the Voltage Efficiency on the main page of the product... So Idk.

    It looks pretty nice, it's got a 400mV dropout voltage, can accept a Input voltage as high as 16v, which I will not be going near, no need too.

    Anyways, please give me some advice, and please try to help if you can. I think I have everything right. I've watched some videos from some very smart users on YouTube (mjlorton).

    Tutorial: How to build and design an AC to DC Power Adapter / Supply
    Link to his video : Here


    That's just a fraction of the stuff I've watched.

    I mainly need help understanding this IC that I've chosen for the circuit I want to build as my first build.

    IMG00000001 2014.10.28 11.00.57 PM.jpg IMG00000001 2014.10.28 09.59.40 PM.jpg
    Thanks :)
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,132
    267
    This part is a LINEAR regulator, it regulates by wasting the excess power so it's not efficient. The efficiency is related to the difference between input and output voltage, the greater the difference, the less efficient it is, that's why it's not specified.
     
  3. Guest3123

    Thread Starter Member

    Oct 28, 2014
    312
    18

    I'm sorry, I'm new to electronics. Does that mean that this will not output 5vdc @ 500mA if I apply 8.4vdc to the input pins? It will dissipate 1.7 watts in wasted energy, .. right?
    That's the LiPo Batteries Maximum charge voltage. It's nominal voltage is 7.4vdc. Which then the IC would dissipate only 1.2 watts, to create the 5vdc @ 500mA output.
    I could use a heatsink designed for the LM7805, I think that should take care of the heat dissipated by the IC.

    I don't think I understand your reply. Can you please.. if you can.. Can you please elaborate?
     
  4. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,132
    267
    Your calculation of power loss is correct. If efficiency is the greatest concern, a switching regulator would be better, some approach 90% efficiency.
    Your design will provide the specified 5V @ 500 ma.
     
  5. Guest3123

    Thread Starter Member

    Oct 28, 2014
    312
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    Do I really need the 10uF Capacitor in the circuit, or could I do without it? Thank you for helping me, and replying back to my question(s).
     
  6. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,132
    267
    As always- read the data sheet for the part, but bypass capacitors are usually required for stability.
     
  7. Guest3123

    Thread Starter Member

    Oct 28, 2014
    312
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    Awesome. Do you know what the maximum current you can charge a cellphone? I was planning on using this one instead for my USB Cellphone Charger.

    Data Sheet : http://www.ti.com/lit/ds/symlink/lm2940c.pdf

    Here's the main product page.

    I'm a little new to electronics, this will be my first electronic circuit. I know how to look at the data sheet, but I still need a little help understanding the specs listed.

    Thanks so much for the help, very much appreciated. :)
     
  8. Sensacell

    Well-Known Member

    Jun 19, 2012
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    The cellphone sets it's own charging current when plugged into USB, the USB port acts as a voltage source with a max current rating of 1 A I believe.
    Some phones will not charge without a handshake of some sort with the USB port- beware.
     
  9. Guest3123

    Thread Starter Member

    Oct 28, 2014
    312
    18
    Ok. So this new LM2940C LDO Voltage Regulator IC says that it requires 22uF. Is this a good leaded Aluminum Electrolytic Capacitor to use on the output of the circuit? Here.

    I also don't understand what you mean by handshake.. I think your talking about the fact that iPhones will not charge if there's not a resistor connected from the GND center pin to the Data + & Data - pins on the USB.. Right?

    If so.. then what resistance would I need, if I owned an iPhone? I don't, my fiancé does. I would like to show her or test this cellphone charger out. But I own a Samsung Galaxy Note 4.
     
  10. Guest3123

    Thread Starter Member

    Oct 28, 2014
    312
    18
    LM2940C in a TO-220 Package.. :)

    This one is really nice too.. It seems.. SPX2940 LDO Voltage Regulator. 5v @ 1.0A

    Here's the main page. Here.
    Here's the data sheet. Here.

    In a TO-220 package of coarse. :)

    IMG00000001 2014.10.29 03.49.13 AM.jpg
    IMG00000001 2014.10.29 03.49.23 AM.jpg
    IMG00000001 2014.10.29 03.49.32 AM.jpg
     
    Last edited: Oct 29, 2014
  11. Guest3123

    Thread Starter Member

    Oct 28, 2014
    312
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    IMG00000001 2014.10.29 03.53.18 AM.jpg

    So happy that I didn't buy any compenents yet.. :)

    Waiting for my paycheck come Friday, then I'll go ahead and buy the components needed to make my first circuit.

    Just amazes me of how much of a selection of different electronic components there is available on "Mouser" & Digitkey.
     
  12. BobTPH

    Active Member

    Jun 5, 2013
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    iPhones will not charge at all unless you put the right voltages on the two data pins. The voltages are different for different models.

    Your Samsung will probably charge at 500mA with nothing on the data lines and at a higher rate with some magic voltages.

    Bob
     
  13. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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  14. ISB123

    Well-Known Member

    May 21, 2014
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    I'd put 800 mA fuse in there just to be safe.
     
  15. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    If you're new to electronics - you *REALLY* don't want to be messing with homebrew lithium chargers!!!!!

    If you overcharge these cells they tend to vent with flaming gas, usually setting fire to anything combustible in the vicinity.

    8.4V suggests more than one cell in series - you *TOTALLY* need the proper charge balancing circuitry to prevent one cell hogging all the charge and venting with flaming gas.
     
  16. BobTPH

    Active Member

    Jun 5, 2013
    784
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    Who said anything about making a lithium battery charger? He is talking about a USB power port powered by a lithium battery.

    Bob
     
  17. Guest3123

    Thread Starter Member

    Oct 28, 2014
    312
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    I'm not charging the LiPo battery, I'm charging the Cellphone battery inside the cellphone threw a USB to micro USB.

    As for the LiPo Battery, I thought about it when I went to go to bed. I'd like to use a cradle from VAPE3D to hold 2x 26650 batteries in parallel, then another VAPE3D cradle to hold another 2x 26650 batteries in parallel. Then hook the two cradles up in series, giving myself (Fullly Charged : 8.4vdc, Nominal : 7.4vdc, at 7,000mAh).


    Lithium Manganese or LiMn (26650 @ 3,500mAh ea.) I use these in my Pure Copper Hades Mechanical Mod.

    IMG00000001 2014.10.29 05.04.53 PM.jpg

    Is this better...?
     
  18. Guest3123

    Thread Starter Member

    Oct 28, 2014
    312
    18
    It seems even with an Android phone, it needs some sort of connection with the D (+) to Vout. Like this guy shows at the end of this video.

    So maybe I'll try different things from the above schematic, or this one shown bellow.

    IMG00000001 2014.10.29 05.20.07 PM.jpg

    Here's the video..

    9 Volt to 5 Volt Phone Charger Tutorial
     
  19. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    Ironically a regular 7805 just drops the right amount and your LDO will do the same thing.

    You probably have your reasons to charge a battery with another battery instead of just powering it with a battery pack.

    Effectively you charge a battery to charge another battery- probably you charge a bag full of them and plan to carry them around or whatever. A 14v battery with a switcher would be better- your batteries just last longer.
     
  20. Guest3123

    Thread Starter Member

    Oct 28, 2014
    312
    18

    Your absolutely correct. But what is a 14v battery with a switcher?
     
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