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does a 9V battery have a current limit?

Discussion in 'Power Electronics' started by dustin02rsx, Feb 8, 2012.

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  1. dustin02rsx

    dustin02rsx

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    May 18, 2011
    its the same thing with with a different part. the caps and Rload in the one in my pic arent necessary... my pic is directly off the data sheet of my LM7812 regulator.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,363
    2,758
    Jan 21, 2010
    OK, fair enough. Your load is Rl (the output shown on that diagram isn't the output)

    The main problem is that it requires about 14V of headroom. You have about 5V (or less). So it won't work.

    Use the one I suggested.
     
  3. dustin02rsx

    dustin02rsx

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    May 18, 2011
    picked up an LM317 today... trying to figure out the best way to power it... i found a 2cr5 battery pack that is 6V recharge able and capable of 1300mah and the data sheet said it lasted for like 1.2 hrs @ 1000mA so i assume that means its safe to run at that current.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,363
    2,758
    Jan 21, 2010
    Yep, that's probably a safe assumption.

    Note that from the original 6V, 1.25 will be dropped across a resistor, about another 2V across the LM317, leaving a maximum of 2.75V for the load. If your LED required more than 2.75V then it's not going to operate at the required current.

    Two of these batteries in series would work, but note that the efficiency of linear current sources can be very low.

    Did I not point you toward some switchmode LED drivers that would be a better choice? Ah yes, I did, but these would work better with a 6V battery.
     
  5. dustin02rsx

    dustin02rsx

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    May 18, 2011
    i always feel like i know what im doing until i post here lol...
    the actual led going into my project requires 2.9Vf.....
    my project is on a very tight space constraint and i think that driver is going to be too big... ill just have to find another power source i suppose...
     
  6. dustin02rsx

    dustin02rsx

    36
    0
    May 18, 2011
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