Reducing Car 12VDC to 10VDC, I need help

Discussion in 'Electronic Design' started by Ron G, May 14, 2005.

  1. Ron G

    Ron G Guest

    Hi---
    Is there an IC that is made for car battery voltage reduction, and is
    "stable" ?
    If I remember, a car system goes up to about 14.4 volts while charging, then
    down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
    winding setup from the ac/dc conversion by the diodes at the alternator.

    I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
    exact mills for sure yet)

    I'm an old geezer that had an associate in Electronics many decades ago, is
    totally outdated, now.
    Any help would be greatly appreciated.
    Thanks in advance! :)

    Ron------


    ---
    Outgoing mail is certified Virus Free.
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    Ron G, May 14, 2005
    #1
  2. Ron G

    John Miles Guest

    In article <>, says...
    > Hi---
    > Is there an IC that is made for car battery voltage reduction, and is
    > "stable" ?
    > If I remember, a car system goes up to about 14.4 volts while charging, then
    > down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
    > winding setup from the ac/dc conversion by the diodes at the alternator.
    >
    > I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
    > exact mills for sure yet)
    >
    > I'm an old geezer that had an associate in Electronics many decades ago, is
    > totally outdated, now.
    > Any help would be greatly appreciated.
    > Thanks in advance! :)
    >
    > Ron------
    >
    >
    > ---
    > Outgoing mail is certified Virus Free.
    > Checked by AVG anti-virus system (http://www.grisoft.com).
    > Version: 6.0.859 / Virus Database: 585 - Release Date: 2/14/05
    >
    >
    >


    Have a look at the supplies sold at http://www.mini-box.com . Chances
    are, one of them will do whatever it is you're trying to do. Their
    stuff works great.

    -- jm

    ------------------------------------------------------
    http://www.qsl.net/ke5fx
    Note: My E-mail address has been altered to avoid spam
    ------------------------------------------------------
    John Miles, May 14, 2005
    #2
  3. Ron G

    Mac Guest

    On Sat, 14 May 2005 12:57:10 -0500, Ron G wrote:

    > Hi---
    > Is there an IC that is made for car battery voltage reduction, and is
    > "stable" ?
    > If I remember, a car system goes up to about 14.4 volts while charging, then
    > down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
    > winding setup from the ac/dc conversion by the diodes at the alternator.
    >
    > I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
    > exact mills for sure yet)
    >
    > I'm an old geezer that had an associate in Electronics many decades ago, is
    > totally outdated, now.
    > Any help would be greatly appreciated.
    > Thanks in advance! :)
    >
    > Ron------


    What you want is readily achievable. The LM117 or LM317 can do it.

    You might even be able to use the TL431. If you only need 20 mA, the TL431
    might be a good choice. If you need more, the LMx17 might be a better
    choice.

    Take a look at the datasheets for these parts and see if you think you
    need more help.

    www.fairchildsemi.com/ds/TL/TL431A.pdf
    http://www.national.com/pf/LM/LM117.html

    Also, note that in general, people don't use "mils" as a measure of
    current. A "mil" is a thousandth of an inch. "Milliampere" is abbreviated
    "mA."

    --Mac
    Mac, May 14, 2005
    #3
  4. Ron G wrote:
    > Hi---
    > Is there an IC that is made for car battery voltage reduction, and is
    > "stable" ?
    > If I remember, a car system goes up to about 14.4 volts while

    charging, then
    > down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
    > winding setup from the ac/dc conversion by the diodes at the

    alternator.
    >
    > I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know

    the
    > exact mills for sure yet)
    >
    > I'm an old geezer that had an associate in Electronics many decades

    ago, is
    > totally outdated, now.
    > Any help would be greatly appreciated.
    > Thanks in advance! :)
    >
    > Ron------
    >


    You want a low dropout regulator. National fixed voltage LM2930, LM2940
    and if you want adjustable, LM2941 will suit you just fine.
    GG
    Glenn Gundlach, May 14, 2005
    #4
  5. Ron G

    CF Guest

    >Also, note that in general, people don't use "mils" as a measure of
    >current. A "mil" is a thousandth of an inch. "Milliampere" is abbreviated
    >"mA."


    People do indeed say "mils" when speaking of mA. They =write= mA,
    but =say= "mils". It's pretty hard to get "mils - mA" mixed up
    with "mils - thousandths of an inch" in a discussion
    CF, May 14, 2005
    #5
  6. Ron G

    Luhan Monat Guest

    CF wrote:

    >>Also, note that in general, people don't use "mils" as a measure of
    >>current. A "mil" is a thousandth of an inch. "Milliampere" is abbreviated
    >>"mA."

    >
    >
    > People do indeed say "mils" when speaking of mA. They =write= mA,
    > but =say= "mils". It's pretty hard to get "mils - mA" mixed up
    > with "mils - thousandths of an inch" in a discussion
    >
    >

    I agree, 'mils' is used between engineers in conversation, so is 'mA'.

    --
    Luhan Monat: luhanis(at)yahoo(dot)com
    http://members.cox.net/berniekm
    "Any sufficiently advanced magick is
    indistinguishable from technology."
    Luhan Monat, May 14, 2005
    #6
  7. On 14 May 2005 12:01:57 -0700, in sci.electronics.design "Glenn
    Gundlach" <> wrote:

    >
    >Ron G wrote:
    >> Hi---
    >> Is there an IC that is made for car battery voltage reduction, and is
    >> "stable" ?
    >> If I remember, a car system goes up to about 14.4 volts while

    >charging, then
    >> down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
    >> winding setup from the ac/dc conversion by the diodes at the

    >alternator.
    >>
    >> I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know

    >the
    >> exact mills for sure yet)
    >>
    >> I'm an old geezer that had an associate in Electronics many decades

    >ago, is
    >> totally outdated, now.
    >> Any help would be greatly appreciated.
    >> Thanks in advance! :)
    >>
    >> Ron------
    >>

    >
    >You want a low dropout regulator. National fixed voltage LM2930, LM2940
    >and if you want adjustable, LM2941 will suit you just fine.
    >GG


    on
    http://www.fordemc.com/docs/p7.html

    ES-XW7T-1A278-AB/C: Component/Subsystem EMC Requirements and Test
    Methods

    Part 3 Figure CI 240 -1, Load Dump Test



    martin

    After the first death, there is no other.
    (Dylan Thomas)
    martin griffith, May 14, 2005
    #7
  8. Ron G

    Guest

    Ron G <> wrote:
    >If I remember, a car system goes up to about 14.4 volts while charging,
    >then down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
    >winding setup from the ac/dc conversion by the diodes at the alternator.


    It can go down lower than 13.8 V, if you're talking about when the
    engine's not running, or if the engine is running but there is a high
    electrical load. A fully-charged car battery at no load is about 12.6 V;
    you'll get less than that at the cigarette lighter socket and less still
    if someone is sitting there with the key off and the radio and dome light
    on, etc. During cranking, most cars go as low as 9.5 V or so at the
    battery and still start. I have heard a suggestion that when designing
    for automotive use, a device should "work" over a 10 V to 15 V range,
    and "survive" 0 V to something well over 15 V, like maybe 30 V or more.

    >I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
    >exact mills for sure yet)


    I second the LM317 suggestion. That's a linear regulator that is good
    for at least 1 amp (in the TO-220 package) with a heat sink; you may not
    need a heat sink or only a very small one for your small demand. IIRC
    the maximum drop through it is about 1.3 V, so for your 10 V
    requirement, the input has to be at 11.3 V or more. If the input is
    less than that, you'll probably get whatever's at the input minus 1.3 V,
    unregulated. In other words, this device won't "work" down to 10 V, but
    that might not be important to you.

    The other option is a DC-DC converter. This is a little brick that
    typically takes a wide range of DC input, chops it into AC, runs it
    through a transformer, rectifies the AC back into DC, and regulates it.
    This will be more expensive than the linear regulator, but will work
    over a wider range of input voltages. The other problem is that a
    10 V output is hard to come by; you could use two 5 V converters and
    wire the outputs in series, or use a 12 V output one and follow it
    with a linear regulator. Basically, what this buys you is operation
    over a wider input voltage range, and a little more isolation from the
    car's electrical system.

    >I'm an old geezer that had an associate in Electronics many decades ago,
    >is totally outdated, now.


    Yeah... They changed which end of a soldering iron to pick up and
    everything. :)

    Matt Roberds
    , May 14, 2005
    #8
  9. Ron G

    mike Guest

    Ron G wrote:
    > Hi---
    > Is there an IC that is made for car battery voltage reduction, and is
    > "stable" ?
    > If I remember, a car system goes up to about 14.4 volts while charging, then
    > down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
    > winding setup from the ac/dc conversion by the diodes at the alternator.
    >
    > I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
    > exact mills for sure yet)
    >
    > I'm an old geezer that had an associate in Electronics many decades ago, is
    > totally outdated, now.
    > Any help would be greatly appreciated.
    > Thanks in advance! :)
    >
    > Ron------
    >
    >
    > ---
    > Outgoing mail is certified Virus Free.
    > Checked by AVG anti-virus system (http://www.grisoft.com).
    > Version: 6.0.859 / Virus Database: 585 - Release Date: 2/14/05
    >
    >


    Before you do anyting automotive, read this.
    http://www.littelfuse.com/data/en/Application_Notes/an9312.pdf

    I'm not familiar with the numeric parameters associated with "nice
    smooth".

    If you expect to get 10V out with ALL automotive conditions, you won't
    get there with a simple linear regulator, LDO or otherwise.

    Whatever you do, make sure you have LOTS of transient protection on the
    input.

    I always caution novice auto power supply designers to weigh the cost of
    the device they're powering against the money you save building your own
    supply. Risking a $2K laptop on a $20 savings in power supply design
    is false economy. YMMV.

    There are also a bunch of other automotive considerations depending on
    what you're trying to do. For example, I've never achieved a power
    suppy for my mp3 player that didn't have excessive ignition and
    alternator whine sneaking thru ground loops.

    mike



    --
    Return address is VALID but some sites block emails
    with links. Delete this sig when replying.
    ..
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    MAKE THE OBVIOUS CHANGES TO THE LINK
    ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/
    mike, May 15, 2005
    #9
  10. Ron G

    Mac Guest

    On Sat, 14 May 2005 17:01:30 -0400, CF wrote:

    >>Also, note that in general, people don't use "mils" as a measure of
    >>current. A "mil" is a thousandth of an inch. "Milliampere" is abbreviated
    >>"mA."

    >
    > People do indeed say "mils" when speaking of mA. They =write= mA,
    > but =say= "mils". It's pretty hard to get "mils - mA" mixed up
    > with "mils - thousandths of an inch" in a discussion


    I have never heard anyone say "mil" when talking about milliamps. Could be
    lack of experience or exposure on my part.

    In any event, I believe my comment still applies to written communication.

    --Mac
    Mac, May 15, 2005
    #10
  11. Ron G

    John Miles Guest

    In article <>, says...

    > I always caution novice auto power supply designers to weigh the cost of
    > the device they're powering against the money you save building your own
    > supply. Risking a $2K laptop on a $20 savings in power supply design
    > is false economy. YMMV.


    Which is why I pointed him at mini-box.com. Whatever your automotive
    power problem, it's safe to say that an LM317T is absolutely NOT the
    solution. :)

    -- jm

    ------------------------------------------------------
    http://www.qsl.net/ke5fx
    Note: My E-mail address has been altered to avoid spam
    ------------------------------------------------------
    John Miles, May 15, 2005
    #11
  12. Ron G

    Fred Bloggs Guest


    > Is there an IC that is made for car battery voltage reduction, and is
    > "stable" ?
    > If I remember, a car system goes up to about 14.4 volts while charging, then
    > down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
    > winding setup from the ac/dc conversion by the diodes at the alternator.
    >
    > I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
    > exact mills for sure yet)
    >


    That would be something like the LM2941C, this is designed to withstand
    the automotive load dump as well as to provide other excellent
    performance characteristics, such as requiring a mere 100mV input-output
    differential at your low load levels. See
    http://cache.national.com/ds/LM/LM2941.pdf and page 8. You will want to
    place a high voltage diode in series between VBATT and Vin to the
    regulator- most applications use 1000PIV- to guard against the
    occasional negative transient on the BATT line. Your regulator will
    dropout during extreme cranking load- but otherwise should work peachy
    keen in every other circumstance.
    Fred Bloggs, May 15, 2005
    #12
  13. Ron G

    Fred Abse Guest

    On Sun, 15 May 2005 06:12:06 +0000, Mac wrote:

    > I have never heard anyone say "mil" when talking about milliamps. Could be
    > lack of experience or exposure on my part.



    "It's volts that jolts, but it's mils that kills"

    --
    "Electricity is of two kinds, positive and negative. The difference
    is, I presume, that one comes a little more expensive, but is more
    durable; the other is a cheaper thing, but the moths get into it."
    (Stephen Leacock)
    Fred Abse, May 15, 2005
    #13
  14. Ron G

    jtaylor Guest

    "Mac" <> wrote in message
    news:p...

    > Also, note that in general, people don't use "mils" as a measure of
    > current. A "mil" is a thousandth of an inch.


    mil = 202.25 arc-seconds, roughly.
    jtaylor, May 16, 2005
    #14
  15. Ron G

    Paul Burke Guest

    jtaylor wrote:
    > "Mac" <> wrote in message
    > news:p...
    >
    >
    >>Also, note that in general, people don't use "mils" as a measure of
    >>current. A "mil" is a thousandth of an inch.

    >
    >
    > mil = 202.25 arc-seconds, roughly.
    >
    >


    'thou' in British usage. "A book of verse, a flask of wine, and 25.4
    micrometres" doesn't quite have the same ring to it.

    Paul Burke
    Paul Burke, May 16, 2005
    #15

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