Recommend me a voltage step up IC/Circuit for USB -> 7-8V

Discussion in 'The Projects Forum' started by TheLaw, Sep 4, 2010.

  1. TheLaw

    Thread Starter Member

    Sep 2, 2010
    228
    2
    Hello,

    I am trying to build a charger circuit for a NiMh battery pack that will hopefully be using with a custom Arduino board.

    I just have one or two questions.

    I am confused as to whether or not USB outputs 100mA or 500mA. I am not sure if it would have an effect on the charger but I was trying to determine that.

    I am trying to charge a 6 pack of Eneloops in series that will be 2000mAH @ 7.2V. After using a step up IC, will I still have enough juice to effectively charge these batteries? I was thinking a fast charger would be good, but trickle is still acceptable.

    So I am trying to find an IC that will step up voltage nicely. I like Mouser.com for ordering stuff, but it doesn't matter.

    I'd like something like this but I can't find anywhere to buy an LTC3458:

    http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1031,C1060,P9230

    Anything else like it?

    Also looking for a decent charger circuit for NiMH if anyone has a recommendation there.

    Thank you very much.

    Have a nice day.

    -Tim
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    USB provides 500mA tops.
    U cannot use this port to charge rates above this without blowing the mobo regulators
     
  3. TheLaw

    Thread Starter Member

    Sep 2, 2010
    228
    2
    Regardless if I use a step up regulator?
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
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    If your software "tells" the motherboard that USB port can source 500 mA that means it can provide 500 mA at 5V = 2.5W

    With a 100% efficient inverter taking 5V to 7.5V would limit the current to 333 mA as 2.5W is 2.5W
     
  5. TheLaw

    Thread Starter Member

    Sep 2, 2010
    228
    2
    Ah....well, I don't want to get that involved. Well, I guess I'll just be hooking up the Arduino via a crappy 300mAH rechargeable. I wonder how long that will last.

    Or just a DC plug in.

    By the way, is there way either by IC or circuit that can enable two power inputs? I was thinking I could have it running off wall DC under most circumstances, but then have it be able to easily switch over to a 9V battery when needed. (Kind of like a laptop?)

    Can anyone give me a pointer to how to achieve that?

    Thanks.
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
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    If losing 0.7V is no big deal just put diodes in series with both supply inputs, that way one can't feed back into the other but either will work as a supply input.
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,740
    759
    If it is easy then tap off the 5V from PC supply.
    Then u can charge any value of li-on's u want
     
  8. TheLaw

    Thread Starter Member

    Sep 2, 2010
    228
    2
    0.7V shouldn't be a problem. Arduino needs 5V and I highly doubt I'd be loose >3V in the power regulation process. :p As for power from the wall, well yeah, that's cool too. Well, they won't be working at the same time will they?
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    With the diodes in there it won't matter anyway, the regulator will just pull current from the source that's presenting the highest voltage.
     
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