9V to 5V voltage regulator..

Discussion in 'The Projects Forum' started by naspek, Aug 29, 2010.

  1. naspek

    Thread Starter Member

    Feb 17, 2010
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    hey guys...
    i'm trying to build 9V to 5V voltage regulator...
    the problem is..
    when i'm using ceramic capacitor, the voltage drop across the capacitor
    was too high,,
    can someone tell me what type of capacitor should be used?
    if possible please provide picture..

    thank u in advance.. =)
     
  2. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
    24
    Can you provide a schematic of your regulator.

    Capacitors appear open circuit to DC so the voltage drop across it will be what ever you apply.

    Is this an input or output capacitor?

    More info please
     
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  3. naspek

    Thread Starter Member

    Feb 17, 2010
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    [​IMG]

    that is my circuit...
    the problem now..
    what type of capacitor should i use?
    ceramic? electrolytic?:confused:
     
  4. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
    24
    Both.

    The 10μF caps should be electrolytic and the .1μF should be ceramic or greencaps or similar. MAKE SURE you get the polarity of the electrolytics right and I would make the ones on the input side 25V and the ones on the output side 16V.

    What is the source of the 9V? Is it a battery or from another DC power supply or straight from a bridge rectifier output? This will also make a difference on the amount of capacitance you need.
     
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  5. naspek

    Thread Starter Member

    Feb 17, 2010
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    0
    ic.. 9V source is from battery...
    i've got electrolytic capacitor, 10uF,25V..
    is it ok?
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    You are also getting a voltage drop from the diode.
     
  7. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Yes. 10μF 25V will be fine. You can use these at both input and output sides. Due to the poor tolerance of electrolytic caps it is always a good rule of thumb to use one with a voltage rating of twice what you are using.

    Also as retched said you will have a voltage drop across the diode. This will be about .7V so i don't think it will be a prblem until the battery voltage drops to about 7V.
     
  8. retched

    AAC Fanatic!

    Dec 5, 2009
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    That is actually what I was thinking.

    9v batteries are notoriously low current sources.

    If this battery is a older, it may be toast. Your 7805 is NOT a LDO, so you need good overhead.. at least 2v.

    So once the battery falls to 7.7v, your about done.

    If you have a battery tester, check the battery.

    Or measure it with your multi-meter.

    If it doesn't read at least 9.8v with no load, it may not be fresh enough to handle this job.
     
  9. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Good points.

    I would also look at getting a schotky diode as well. 0.2V drop so you get an extra 0.5V to play with.

    Also, if you are 100% positive you won't reverse the polarity of the battery do away with the diode. NOTE: 100% positive
     
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    With your multi-meter, measure the voltage with the RED probe on the RED dot and the BLACK probe on the BLUE dot. ALSO, make sure the battery polarity is correct, and the electrolytic capacitors polarity is correct.

    [​IMG]
     
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