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Thread: 3 Volts from 12-19 Volts

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    Default 3 Volts from 12-19 Volts

    Hi Guys,
    I need a regulated 3 V supply from a 12 - 19 Volt supply in a small device if possible..
    like a 7805, bu tI know there's nothing in that family.
    It's to power a digital camera externaly from cig lighter, and solar panel.
    Any pointers?



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    There is a 7803 fixed regulator or a LM117/LM317 is an adjustable 3 terminal regulator down to 1.2v

    The National Semiconductor web site has a "designer" try it out..

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    There is a switch mode DC DC converter from Jaycar
    MP-3014 for around $25.
    11-30V in and various voltages in 1.5V steps including 3V out.

    I would not use a linear regulator like LM317 etc or even bother building something like that.
    Many digital cameras have a high current drain, often more than 1A.
    You might need a fairly large heat sink and if you intend to use it from a solar panel you could be wasting 15W for a camera that needs 3W.

    The switch mode will use far less power and I have a gut feeling that you might find use for the other voltage settings as well

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    Thanks, I actually had one of those Jaycar ones built into a lighter adapter,
    with the selectable output and all, pity I can't find it. It was the first thing to come to mind.
    If I remember correctly it was rated between 1 and 1.5 Amp.
    I was hoping for something smaller and hopefully cheaper, and didn't know there was a 7803 regulator at all.
    Yes it is high current drain, but only in use for short periods at a time,
    considering I've got to buy something, maybe I'll get away with it.

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    Quote Originally Posted by ssrattus View Post
    There is a 7803 fixed regulator or a LM117/LM317 is an adjustable 3 terminal regulator down to 1.2v

    The National Semiconductor web site has a "designer" try it out..

    27 years in the electronics industry and I never knew there was a 7803!

    Jeez.. ya learn somethin' new every day...

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    Quote Originally Posted by Studio1 View Post
    27 years in the electronics industry and I never knew there was a 7803!

    Jeez.. ya learn somethin' new every day...
    With further research I can't find a 7803 mentioned anywhere.

    Wikipedia says there are 3V fixed three terminal regulators, so maybe it exists in some form somewhere.

    Fixed regulators

    "Fixed" three-terminal linear regulators are commonly available to generate fixed voltages of plus 3 V, and plus or minus 5 V, 9 V, 12 V, or 15 V when the load is less than about 7 amperes.

    The "78" series (7805, 7812, etc.) regulate positive voltages while the "79" series (7905, 7912, etc.) regulate negative voltages. Often, the last two digits of the device number are the output voltage; eg, a 7805 is a +5 V regulator, while a 7915 is a -15 V regulator.
    Probably easier to just use the LM317 3 terminal adjustable, only a couple extra resistors needed over fixed regulator, but the case isn't ground.

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    Maybe those voltage selector lighter adapters work by switching through a
    resistor ladder with one of those variable regulators.

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    Art, a linear regulator like the LM317 will have to dissipate over 16watts @1.5A from a battery with 13.8V to regulate down to your 3V.
    The heat sink would have to be bigger than what can physically fit inside those adaptors unless it uses a little fan.

    As a ball figure a newer style camera might be consuming around 0.5 amp while you are selecting a picture, 1 amp while doing a movie clip and possibly 2 amps while it is recharging the flash.
    So if you have the camera on for only 2 mins with 10-15mins break you might get away with an underrated heat sink, but such a device would certainly not be offered for sale (with the tick).

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