voltage regulator

Discussion in 'General Electronics Chat' started by Natsoumi, May 2, 2009.

  1. Natsoumi

    Thread Starter New Member

    Apr 2, 2009
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    hi,

    im trying to provide power to my PCB using a 9V battery. however, the 10 pins on the left use 3.3V and the 10 pins on the right use 5V. I know i should use a voltage regulator to do so, but im afraid that my circuits basics are not that good.

    could someone plz explain to me how the voltage regulator circuit should be connected.

    oh, and the voltage regulator im using is the LM7805

    Thank you for your time,
    NM
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Do you have a schematic of the PCB you are trying to give power?
    You say you need 5 Volts and 3.3 Volts , that puzzles me.

    Greetings,
    Bertus
     
  3. Natsoumi

    Thread Starter New Member

    Apr 2, 2009
    9
    0
  4. Natsoumi

    Thread Starter New Member

    Apr 2, 2009
    9
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    here is the VDIP2's image....i hope u can c it :S

    [​IMG]
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    As far as I can see there is only 5 Volts used.
    The 3.3 Volts is made on the board itself from the 5 Volts input.
    The 5 Volts must be connected to pins 2,3 and 9.
    The Ground connection to pins 12,13,15 and 26.

    You can use the 5 volts regulator.
    I do not know how long a 9 volts battery will last.
    There is stated in the PDF the 3.3 volts may deliver 200 mA, wich is quite a lot for a 9 volts battery.

    Greetings,
    Bertus
     
  6. Natsoumi

    Thread Starter New Member

    Apr 2, 2009
    9
    0
    thnx for clearing that up for me...i didn't realize the 3.3v were output XD

    so, i just have to supply the 5v...the battery doesn't have to last for a long time....just long enough for my demo presentation (around 10-20 minutes)

    so will my voltage regulator part of the circuit be something like:

    battery->voltage regulator->appropriate resistor->PCB
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    You can use the schematic used in the 78XX datasheet.

    [​IMG]

    Greetings,
    Bertus
     
  8. Natsoumi

    Thread Starter New Member

    Apr 2, 2009
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    thank you very much bertus ^_^
     
  9. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    As bertus says all you need is a 5 Volt input, the 3.3 Volt is an output from the board.

    One point I would make is that if you are using a 9 Volt battery I would not use an LM7805 regulator. The LM7805 has a dropout voltage of 2 Volt which means that it needs 2 volts dropped across the regulator for it to work. Once your on load battery voltage drops to 7 volt the regulator will turn off. This will give very poor battery life.

    Instead I would go for a low dropout regulator such as an LM2931-5 or LM2937-5 which have a dropout voltage of about 0.5 Volt so the regulator will keep working till the battery voltage falls to about 5.5 Volt.
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    The LDO is a good option AlexR.
    For longer use of the circuit you could also replace the 9 volts battery by a pack of 6 1.5 Volts batteries like , AA, C or even D cells.

    Greetings,
    Bertus
     
  11. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I was about to suggest making 9V using "AA" batteries, it is still small but will last much longer.
     
  12. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
    907
    It's a 20-minute demo. Four, 2300 mAh AA NiMH batteries would give you a pretty steady voltage of 5.2'ish to 4.8 at 2.3A for that period -- maybe even better, if your current drain isn't much. Or, you might even consider four, 1000 mAh AAA batteries.

    What are your current requirements?

    John
     
  13. Natsoumi

    Thread Starter New Member

    Apr 2, 2009
    9
    0
    guyz thank u very much for your VERY helpfull answers and suggestions...i really appreciate it =D


    i have no idea =S
     
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