LDO Alternative to LM317

Discussion in 'General Electronics Chat' started by iONic, Jul 28, 2011.

  1. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
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    As amazing as it seems I am having trouble locating an alternative Linear Voltage regulator for the LM317 with a Lower Drop Out Voltage and adjustable Output Voltage (Target 13.8V) and Current (Target - 400mA - 1.5A). Anyone care to take a quick look for me.

    Appreciate it!
     
  2. SgtWookie

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    Jul 17, 2007
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    Why don't you go for a switching regulator solution instead?

    What's your input source (volts, amps), and what's the AH size of the battery/batteries you're planning on charging?
     
  3. praondevou

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    Jul 9, 2011
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    The datasheet of the LM317 I have shows a dropout voltage at max output current of more than 2.5V.

    The LD1086 series from ST and the LT1083 through LT1086 adjustable regulators from Linear Technology have at most 1.5V.


    There are quite a few of them on digikey.
     
  4. nickelflipper

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    Jun 2, 2010
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    Also the LM1117 with assorted limitations, 1.2V at 800ma max output, 20V max input.
     
  5. iONic

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    Nov 16, 2007
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    That could very well be a better idea. Nice assumption about battery charging, or in this case Float Charging. I was looking at the Temperature Compensated Float Charger you posted recently using the LM317 and wanted to make a more efficient one for use with batteries with a range of AH ratings, but more specifically for the float charger for the Battery Desulfator.

    The AH rating might be for anything from a 12AH to 35AH to even a small deep cycle battery for my solar array. This is why I was interested in a selectable output current limit.
    The power supply: I have three that should meet the necessary requirements.

    1) 16V, 3.36A
    2) 16V, 2.20A
    3) 20V, 3.00A

    All are switching power supplies.
     
  6. iONic

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    Nov 16, 2007
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    Right at the very limits of operation and not functional for the wide range I am hoping for...Thanks for the suggestion.


    The LT1085 with 1.0V DropOut looks like a possible candidate.

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    Now let me look at the task from a different perspective. Instead of having 2, 3, 4,... Float chargers plugged into the wall, Why not just tap off a single deep cycle battery, already DC and design a system where one could parallel the Float Charge Voltage & Current to several batteries of similar float requirements. Think this is possible. Then I could charge a single battery in order to repeat the process.
     
    Last edited: Jul 29, 2011
  7. SgtWookie

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  8. iONic

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    I think the LT1085 for the Desulfator, but I will do some reading on that TI IC
    the BQ2031. Thanks Sgt.
     
  9. SgtWookie

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    If you're using the desulfator schematic I put up, the charge circuit should be less than 2A, and less than that depending upon the inductor you used.

    The charger has to be connected across the big cap(s). This also means that any charge current must flow through the 1000uH inductor; the DC bias will reduce its capacity, as the DC establishes a magnetic field around the core. If your inductor was marginal to begin with, you will wind up saturating it when the MOSFET turns on.

    I suggest that you get the battery charged before you start the desulfation process.
     
  10. iONic

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    Yes, I would normally attempt a full charge on battery in prep for desulfation.
     
  11. iONic

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    Is there a relationship between a batteries AH rating and the float charge current or is it primarily based on the Batteries voltage, ie 12V, 6V...

    Google has not been so friendly with this question.
     
  12. k7elp60

    Senior Member

    Nov 4, 2008
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    There is a 3 terminal IC specific for 12V lead-acid batteries it is a PB137, another low dropout is the LT1083CP, good for about 8A I have extra of the LT1083CP if you could use it.
     
  13. iONic

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    The PB137 is a nice find, pretty neat.
    As far as the LT1083CP I was planning on using the LT1085 (3A) Version, but I suppose the 8A version would be identical given the power supply I would use would not provide more than 3.5A - 4.0A.
     
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