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12V DC to 9V DC

Discussion in 'Electronic Repair' started by Bart Bervoets, Jul 21, 2006.

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  1. Power resistor or voltage regulator?
    Anyone a simple diagram?(if i need one)
    Draw is about 1A but i would like to have some tolerance.

    Bart Bervoets
  2. me

    me Guest

    a pretty good site (but everyone here has probably seen it before).
    A resistor would work if the current draw is fairly constant, but 3
    terminal voltage regulator (LM7809 eg.) is better. circuit is regulator and
  3. Dave D

    Dave D Guest

    ....and caps from input and output pins to ground pin to prevent


  4. This kind of question should be asked on:

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  5. James Sweet

    James Sweet Guest

    Use a 7809 regulator, a resistor will only work if the device has a
    constrant draw and the voltage in is constant, which is almost never the
  6. Regulator. Probably something like an L78S09CV which is a 2 amp type. Do a
    search on it and you'll find a data sheet which will give the circuit
    diagram. Additional components are two electrolytics, two disc capacitors
    and a couple of diodes for extra protection.
  7. Arfa Daily

    Arfa Daily Guest

    I don't wish to get into another of those push and shove contests that I had
    with you last year, but would you care to tell us all why the poster *
    should *, in your opinion, have asked his question elsewhere ? Yes, it is a
    basic question, and yes, the group that you cite would be a valid place to
    ask that question, but no more so than here. This person regularly posts on
    this group, and I see no problem with his asking this question here. He has
    received a number of valid replies, and no one bar you, is objecting to the
    simple nature of the question.

    Maybe it's your military bearing that makes you prone to giving out with
    these bluff statements. It might have been more appropriate to have made
    your comment along the lines of " this question * could also * be asked on
    blah blah blah, just so that posters know that such a place exists.

    A couple of weeks ago, a person posted a warning to this group, saying that
    anyone who asks a naiive question on here was likely to be attacked as a
    fool. I went to great lengths to defend the people who regularly post help
    on here, saying that many such questions were posed, and with the exception
    of those where the poster seemed to be implying that he was trying to work
    with dangerous kit without the necessary safety knowledge, replies would be
    polite and helpful. Your telling Bart that he should be posting elsewhere,
    implying that his question is too simple for the likes of this group, flies
    in the face of that.

    It may be that you have no intention of sounding "superior", but if that is
    the case, may I respectfully request that you remember that this is an
    international group, and the "bold American way" may not always come over in
    other parts of the world, as sounding very polite.


  8. I pointed out the other group, becasue they are less likely to be
    abused there, and there a lot of EEs who are willing to draw up simple
    schematics to explain things. That is what the group was created for.
    I don't object to it being asked here, but the OP might find more or
    diffferent help there, as well as meet others who are wanting to learn
    more about electronics.

    I tell some people who ask very basic questions on
    the same thing, and for the same reasons.
    Why go to a Chevy newsgroup to ask about Ford problems? Also, if
    someone is using Google to look for information before they post, it
    helps to have it all in one place.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  9. A resistor is easiest if the supply voltage and current draw
    are fairly constant. You didn't indicate what sort of
    device you are trying to power; some are much more forgiving than others.

    Voltage divided by Current = Resistance
    (3 volt drop/1 ampere = 3 ohm resistor)
    Current squared times resistance = power in watts
    (1 x 1 x 3 = 3 Watt resistor - get a 5 watt for safety)
    So you need a 3 ohm 5 watt resistor
  10. Creative labs pc speakers in my car.
    And for 2 amps?
    I don't really understand your calculation as i am useless in math.

    Bart Bervoets
  11. Dave D

    Dave D Guest

    Forget it, a resistor is useless for your application. You'll need to build
    a decent voltage regulator circuit to power such gear if you want it to
    work well.

    You may find the speakers work just fine at 12V ( or more like 13.8V or
    higher if we're discussing a car's power supply), it's up to you whether you
    want to risk finding out!

  12. Arfa Daily

    Arfa Daily Guest

    This kind of question should be asked on: news:sci.electronics.basics
    OK Michael, all fair enough comment. Sorry, I'm probably being a bit
    sensitive about your American way of saying things. It was just that it
    sounded a bit dismissive to the guy, who is, after all, a regular poster
    here. Thanks for the polite reply. Appreciated.


  13. I also point people here when they ask repair questions on the other
    sci.electronics groups to make sure they find the help they need. Its
    not to say the OP couldn't get help here, but its not something normally
    dealt with here. My replies are rather short at times, because of pain
    in my hands prevent me from doing a lot of typing.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  14. Aw c'mon, admit it, you're just a crotchety old fart...

    Seriously, how are you doing lately? Are you still in the Ocala area?


  15. You're just jealous because you have to behave in front of your
    customers. ;-)

    Not too well. I can't get my blood sugar back down this time, and
    the prescription pain killers no longer work at all. Yes, I'm still in
    the Ocala area. How is your CET coming along? I don't get on here too
    often anymore and I may have missed something.
  16. Have not had time to even bother with the CET. Been busy with work and the
    kids. Keeping good help is nearly impossible. Getting a bit crotchety
    myself, maybe. Or just less tolerant of stupid. Be well. Be in touch.
    Give me a call at the shop sometime.


  17. I know all too well how you feel about stupid. I see more than my
    fair share, too. :(

    I don't have long distance service, but I'll try to call you the next
    time I'm at the VA hospital for tests. Probably a couple months before
    they find a reason to send me back to Gainesville.

    BTW, my Email address is good.
  18. I can remember when sci.electronics was the newsgroup, with only as a separate group. I don't recall it being too busy,
    but it was getting there, and some decided it was worth splitting, so they
    went through the process, and it passed, so now we have a slew of newsgroups
    instead of just sci.electronics

    In other words, it was decided to break things down into more specific and
    manageable sub-groups.

    Once again, see Mark Zenier's guide to the hierarchy at
    Mark was one of the main people to take care of the process of
    splitting sci.electronics, it was back in 1995 or maybe 96.

    By your process, you might as well have One Big Newsgroup, so every one
    sees everything that people are posting. The problem is that it would
    be way too cumbersome, so instead we have all kinds of newsgroups that
    are devoted to smaller and smaller specialties.

    The notion that newsgroups are places where people "hang out" is a dangerous
    one. Because once you start letting people ask off-topic questions simply
    because they "know the other posters", then it's just a small leap until
    all kinds of off-topic stuff is posted. Witness
    where not only are there too many beginner's questions (and no, that's
    not superiority, it's a case of the regulars there taking the questions too
    literally and thus not supplying a proper answer to a beginner, and too
    often we are seeing people posting there simply because it has more traffic
    than the other newsgroups, which the split was about avoiding), but first we
    had the weather reports and then the Girl Guide reports and then just about
    anything goes. It's simply a case of some people deciding it's a hang out,
    but instead of hanging out to discuss the topic at hand, they never go
    anywhere else, instead discussing all their off-topic matters there, rather
    than moving to a newsgroup where such discussions fit. There are plenty of
    places where the other topics fit, and indeed there are plenty of newsgroups
    where "community" fits, like all those local newsgroups. Don't ever forget
    that these newsgroups travel the world, and for the rest of us, we
    aren't interested in reading about politics or seeing ads or
    some other location specific post that has little relevance to the rest
    of us; if we wanted to read such things, we'd go to the appropriate
    newsgroups. And that's no different from seeing someone asking about
    building something in a repair newsgroup; some of us do happen to
    read both newsgroups, but that is secondary to the fact that we are
    reading each for two different purposes.

    The same thing with the too common cross-posting, people shotgunning
    their question around because they can't be bothered to find the most
    appropriate newsgroup. It does not work in their favor, because people
    like me do think carefully about replying to something cross-posted,
    so the poster may not get an answer that they would have gotten if
    they posted to the right newsgroup in the first place. And yes,
    I will think twice about replying to a question in the wrong newsgroup,
    and indeed from now on I will pay even more attention to this matter.
    And so if I tell someone they should ask it elsewhere, that would
    be the only way they'll get an answer from me, by moving to the right

    And is just a way station. I can recall when it
    started heading that way, and I could point you to newsgroups where it
    is far worse, where any time someone asks an on-topic question, it very
    quickly dissolves into the handful of regulars talking among themselves,
    too often in a competition to see who can have the wittiest comment. If
    you think someone telling someone else to post somewhere else where it
    is more appropriate is being "superior", then just wait till this newsgroup
    devolves to the point where a handful of regulars have decided the newsgroup
    is not what the charter says it's for, but for their own personal space.

    I should point out that Michael is not imposing his will on this matter,
    simply following how the sci.electronics.* hierarchy is supposed to work.
    I should point out that Mark Zenier used to post the guidelines on a regular
    basis, until someone gave him flack for it, at which point he stopped. Is
    should point out that Clifton Sharpe used to make a point of pointing out
    that ads didn't belong, and while I don't know if he lost interest or
    felt driven off, but it's been some years since I can recall seeing a
    post of his. I know I've pointed out quite blatant advertising or
    off-topic posts sometimes over the years, but even though it does work,
    because it helps to ensure that others don't follow the bad examples,
    it's not something that gets rewarded, and it's easier to stop doing it
    than continue. And then the newsgroups start sliding towards uselessness,
    and by the time it becomes really blatant, it's too late because too many
    of the good posters have left.

  19. Rather not, i will build that litte circuit.
    The transformer has 9V for a reason.

    Bart Bervoets
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