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Getting 5VDC from a 9 volt battery

Discussion in 'Electronic Basics' started by PIC, Feb 6, 2004.

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  1. PIC

    PIC Guest

    Hi,

    Is there an easy, efficient, and low cost way to get 5VDC to power a
    microcontroller (PIC16F77) from a standard 9 volt battery? If you need more
    information, please feel free to ask.

    Thanks in advance,
    Joe
     
  2. The simplest would be a linear regulator. The NPN output types are
    most stable, but waste a bit more power and need about 1.5 volts above
    the 5 volt output to work.

    Here is a list of all those made by National Semiconductor:
    http://www.national.com/parametric/0,,648,00.html

    A good candidate for a PIC and very little else (low current) might be
    the LM340LAZ-5.0 or the LM78L05. Both are good for 100 ma out, which
    is more than you can say for a 9 volt battery.

    The low drop out types are listed here:
    http://www.national.com/parametric/0,1850,663-c14-0,00.html

    They work till the battery gets very close ot 5 volts, so they last a
    bit longer (but not much, since a 9 volt battery goes down very
    quickly once it reaches 7 volts).
    The LM2936-5.0 is good for up to 50 ma.
    The LM2931 series are good for 100 ma.
    The low drop out types are also more particular about capacitor
    filtering to remain stable than the NPN output types, so unless you
    have a scope to verify that they are not oscillating, I recommend you
    go with a low current version from the first list.

    The data sheets for all these are available from these lists, so you
    can review all the particulars.
     
  3. Don Bruder

    Don Bruder Guest

    A 7805 voltage regulator mounted on a hefty heat-sink is probably the
    simplest and cheapest, but I'd expect it to chow on batteries like
    they're being outlawed tomorrow.

    This is one of those classic "You have three options: Easy, Cheap, and
    Efficient. You may choose any two of them" situations. You want easy and
    cheap, you gotta give up efficient. You want efficient, figure out which
    of easy and cheap is more important to you and kiss off the other one.
     
  4. Beowulf

    Beowulf Guest

    I know very little about electronics, but I successfuly
    built this gaussmeter which is stupidly simply to build
    and it drops a 9V transistor battery to 5V DC using a
    cheap simple voltage regulator.
    http://my.execpc.com/~rhoadley/magmeter.htm
     
  5. Byron A Jeff

    Byron A Jeff Guest

    -Hi,
    -
    -Is there an easy, efficient, and low cost way to get 5VDC to power a
    -microcontroller (PIC16F77) from a standard 9 volt battery? If you need more
    -information, please feel free to ask.

    I'm glad you put efficient into the equation. Simply put any linear regulator
    is going to consume almost half of your already meager power budget.

    You need a switching regulator. You can get 2.5 out of your 3 requirements
    by using the Roman Black 2 transistor switching regulator here:

    http://www.romanblack.com/smps.htm

    It has nearly double the efficiency of the linear regulator and will maintain
    regulator down a lower voltage, so it'll run over twice as long as the
    linear regulator. It's not a single part (so only half for easy) but it is
    cheap and very very efficient.

    BAJ
     
  6. j taylor

    j taylor Guest

    what is wrong with using 4 nicads? they add up to 4.8 volts
     
  7. The smps you recommend is nice, but if the OP is doing any analog
    measurements, the noise from the smps might interfere.

    Depending on the application, its possible that a linear regulator is fine
    for the tiny amounts of current required for a PIC.

    Regards,
    Bob Monsen
     
  8. Byron A Jeff

    Byron A Jeff Guest

    -
    -> In article <>,
    -> -Hi,
    -> -
    -> -Is there an easy, efficient, and low cost way to get 5VDC to power a
    -> -microcontroller (PIC16F77) from a standard 9 volt battery?

    -> You need a switching regulator. You can get 2.5 out of your 3 requirements
    -> by using the Roman Black 2 transistor switching regulator here:

    -what is wrong with using 4 nicads? they add up to 4.8 volts

    Nothing. However that wasn't the question asked.

    BAJ
     
  9. Byron A Jeff

    Byron A Jeff Guest

    -
    --> In article <>,
    -> -Hi,
    -> -
    -> -Is there an easy, efficient, and low cost way to get 5VDC to power a
    -> -microcontroller (PIC16F77) from a standard 9 volt battery? If you need
    -more
    -> -information, please feel free to ask.
    ->
    -> I'm glad you put efficient into the equation. Simply put any linear
    -regulator
    -> is going to consume almost half of your already meager power budget.
    ->
    -> You need a switching regulator. You can get 2.5 out of your 3 requirements
    -> by using the Roman Black 2 transistor switching regulator here:
    ->
    -> http://www.romanblack.com/smps.htm
    ->
    -> It has nearly double the efficiency of the linear regulator and will
    -maintain
    -> regulator down a lower voltage, so it'll run over twice as long as the
    -> linear regulator. It's not a single part (so only half for easy) but it is
    -> cheap and very very efficient.
    ->
    -> BAJ
    -
    -The smps you recommend is nice, but if the OP is doing any analog
    -measurements, the noise from the smps might interfere.

    Low noise wasn't a part of the specification. Efficient was.

    -
    -Depending on the application, its possible that a linear regulator is fine
    -for the tiny amounts of current required for a PIC.

    Truthfully 9V batteries are not the best for many applications. They end up
    being a string of AAAA cells, which really do not have a whole lot of power.
    D cells typically have over 10 times the capacity of equivalent 9V batteries.
    It may be better to think about how to take 2 D cells giving 3V and boost it
    to 5V.

    BAJ
     
  10. You are right, but many folks use the PIC analog to digital converter. The
    OP may not understand the noise implications of using an SMPS. I was simply
    pointing out that the solution you suggested could interfere with that
    possible usage.
    The nice thing about 9V batteries is that they are quite compact, and very
    easy to interface with. You don't need a special battery holder, you only
    need a two wire connector and a little compartment in your enclosure.

    Regards
    Bob Monsen
     
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