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Re: [Electronics_101] Slowing down voltage

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  • robert wong
    Hi JOn, I have a LM317 in TO220 package that I intend to build a 1.5 - 35v / 1.5amps variable regulated power supply for testing my hobby electronic circuits.
    Message 1 of 20 , Aug 10, 2001
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      Hi JOn,
       
      I  have a LM317 in TO220 package that I intend to build a 1.5 - 35v / 1.5amps variable regulated power supply for testing my hobby electronic circuits. The transformer is 230AC50~/32-0-32v rated at 3 amps.  Do you have a circuit that I can used?  
       
      Appreciate help from you and regards.
        
      Bob Wong - Singapore
      ----- Original Message -----
      Sent: Friday, August 10, 2001 9:45 AM
      Subject: Re: [Electronics_101] Slowing down voltage

      Hi,
          First - a little more information - at what amperage (current) do you
      need this voltage? It's reasonably important.

      There are a couple of ways you can do it, either with a LM317 positive
      voltage regulator (and a by-pass transistor if you need a higher current),
      or a Zener Diode / NPN transistor combination.

      Regards,


      J0n

      ----- Original Message -----
      From: <ifugeri@...>
      To: <Electronics_101@yahoogroups.com>
      Sent: Friday, August 10, 2001 10:31 AM
      Subject: [Electronics_101] Slowing down voltage


      > I need to slow down 12VDC to 4.5VDC, what do I need to accomplish
      > this?
      >
      >
      >
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    • Ed Jacobson
      What do you want to do with the 4.5V? Get your FREE download of MSN Explorer at http://explorer.msn.com
      Message 2 of 20 , Aug 10, 2001
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        What do you want to do with the 4.5V?


        Get your FREE download of MSN Explorer at http://explorer.msn.com
      • Tim
        Hi, I know this reply is coming 3 years after the original post but... just a quick question for anybody because I don t understand... Why couldn t someone
        Message 3 of 20 , May 6, 2004
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          Hi,

          I know this reply is coming 3 years after the original post but...
          just a quick question for anybody because I don't understand...

          Why couldn't someone just use a resistor to drop the voltage?
          Wouldn't that be the simplest way? Would it get too hot dropping
          that much voltage? Is it not the most reliable way to get a constant
          output?

          Any comments would be appreciated.. thanks

          Tim

          >
          > > I need to slow down 12VDC to 4.5VDC, what do I need to accomplish
          > > this?
          > >

          --- In Electronics_101@yahoogroups.com, "Jonathan Luthje"
          <jluthje@p...> wrote:
          > Hi,
          > First - a little more information - at what amperage (current)
          do you
          > need this voltage? It's reasonably important.
          >
          > There are a couple of ways you can do it, either with a LM317
          positive
          > voltage regulator (and a by-pass transistor if you need a higher
          current),
          > or a Zener Diode / NPN transistor combination.
          >
          > Regards,
          >
          >
          > J0n
          >
          >
        • Stefan Trethan
          ... well, if the load current is constant, and the supply voltage is constant (the 12V), then it would work. if one of them varies the output of the resistor
          Message 4 of 20 , May 6, 2004
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            On Thu, 06 May 2004 16:11:03 -0000, Tim <rowanbeef@...> wrote:

            > Hi,
            >
            > I know this reply is coming 3 years after the original post but...
            > just a quick question for anybody because I don't understand...
            >
            > Why couldn't someone just use a resistor to drop the voltage?
            > Wouldn't that be the simplest way? Would it get too hot dropping
            > that much voltage? Is it not the most reliable way to get a constant
            > output?
            >
            > Any comments would be appreciated.. thanks
            >
            > Tim

            well, if the load current is constant, and the supply voltage is constant
            (the 12V),
            then it would work. if one of them varies the output of the resistor would
            not be constant.
            The power drop is not a problem, it is only a question of size of the
            resistor.

            If something changes over time, and you still need a constant output, then
            you need
            some sort of stabilizing circuit (The value of the resistor would need to
            change over
            time to counteract the changes of voltage/current. this is what happens in
            a semiconductor
            "automatically", it has a non-linear behavoir)

            ST
          • Roy J. Tellason
            ... The other aspect that s not being considered here is efficiency. If I have a circuit where the maximum voltage of a motor is half of the supply voltage,
            Message 5 of 20 , May 6, 2004
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              On Thursday 06 May 2004 01:45 pm, Stefan Trethan wrote:
              > On Thu, 06 May 2004 16:11:03 -0000, Tim <rowanbeef@...> wrote:
              > > Hi,
              > >
              > > I know this reply is coming 3 years after the original post but...
              > > just a quick question for anybody because I don't understand...
              > >
              > > Why couldn't someone just use a resistor to drop the voltage?
              > > Wouldn't that be the simplest way? Would it get too hot dropping
              > > that much voltage? Is it not the most reliable way to get a constant
              > > output?
              > >
              > > Any comments would be appreciated.. thanks
              > >
              > > Tim

              > well, if the load current is constant, and the supply voltage is constant
              > (the 12V), then it would work. if one of them varies the output of the
              > resistor would not be constant. The power drop is not a problem, it is only
              > a question of size of the resistor.
              >
              > If something changes over time, and you still need a constant output, then
              > you need some sort of stabilizing circuit (The value of the resistor would
              > need to change over time to counteract the changes of voltage/current. this
              > is what happens in a semiconductor "automatically", it has a non-linear
              > behavoir)

              The other aspect that's not being considered here is efficiency. If I have a
              circuit where the maximum voltage of a motor is half of the supply voltage,
              then with a resistor half of the power supplied to that motor is going to be
              dissipated in the resistor -- as heat. If, OTOH, I use a chopper to give
              the power a 50% duty cycle, then the motor ends up getting only half of the
              power it would otherwise. Heat dissipation is minimized if switching is fast
              enough as the waveform spends relatively little time transitioning through
              the lnear regions and most of its time either saturated or cut off. It's the
              same reason that switching power supplies are so much more efficient.
            • Stefan Trethan
              ... doubt that. ST
              Message 6 of 20 , May 6, 2004
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                > It's the
                > same reason that switching power supplies are so much more efficient.

                doubt that.

                ST
              • Stefan Trethan
                On Thu, 06 May 2004 20:08:35 +0200, Stefan Trethan ... sorry, did rethink it... if you compare switching supply to linear supply then
                Message 7 of 20 , May 6, 2004
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                  On Thu, 06 May 2004 20:08:35 +0200, Stefan Trethan <stefan_trethan@...>
                  wrote:

                  >
                  >> It's the
                  >> same reason that switching power supplies are so much more efficient.
                  >
                  > doubt that.
                  >
                  > ST
                  >

                  sorry, did rethink it... if you compare switching supply to linear supply
                  then it is of
                  course true. but you can't compare it to e.g. a 60hz transformer.

                  ST
                • Phil
                  It also depends on why they are dropping from 12 to 4.5. If its for power, then a regulator is called for since the load is likely to vary. If its for a
                  Message 8 of 20 , May 6, 2004
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                    It also depends on why they are dropping from 12 to 4.5. If its for
                    power, then a regulator is called for since the load is likely to
                    vary. If its for a signal input with low draw then a dropping
                    resistor is the right solution.

                    Also, if using a regulator and drawing above 100 mA or so, thats a
                    largish drop. There may be a heat dissipation problem. If using a
                    linear regulator, like the lm317 for example, a heat sink would be
                    called for. Better would be a switching or buck regulator

                    By the way, "slowing down voltage" is a non-sequiter unless we are
                    talking about changing the speed of light. But the speed of light
                    isn't just a good idea, ITS THE LAW. sorry, couldn't resist.

                    --- In Electronics_101@yahoogroups.com, "Roy J. Tellason"
                    <rtellason@b...> wrote:
                    > On Thursday 06 May 2004 01:45 pm, Stefan Trethan wrote:
                    > > On Thu, 06 May 2004 16:11:03 -0000, Tim <rowanbeef@y...> wrote:
                    > > > Hi,
                    > > >
                    > > > I know this reply is coming 3 years after the original post
                    but...
                    > > > just a quick question for anybody because I don't understand...
                    > > >
                    > > > Why couldn't someone just use a resistor to drop the voltage?
                    > > > Wouldn't that be the simplest way? Would it get too hot
                    dropping
                    > > > that much voltage? Is it not the most reliable way to get a
                    constant
                    > > > output?
                    > > >
                    > > > Any comments would be appreciated.. thanks
                    > > >
                    > > > Tim
                    >
                    > > well, if the load current is constant, and the supply voltage is
                    constant
                    > > (the 12V), then it would work. if one of them varies the output
                    of the
                    > > resistor would not be constant. The power drop is not a problem,
                    it is only
                    > > a question of size of the resistor.
                    > >
                    > > If something changes over time, and you still need a constant
                    output, then
                    > > you need some sort of stabilizing circuit (The value of the
                    resistor would
                    > > need to change over time to counteract the changes of
                    voltage/current. this
                    > > is what happens in a semiconductor "automatically", it has a non-
                    linear
                    > > behavoir)
                    >
                    > The other aspect that's not being considered here is efficiency.
                    If I have a
                    > circuit where the maximum voltage of a motor is half of the supply
                    voltage,
                    > then with a resistor half of the power supplied to that motor is
                    going to be
                    > dissipated in the resistor -- as heat. If, OTOH, I use a chopper
                    to give
                    > the power a 50% duty cycle, then the motor ends up getting only
                    half of the
                    > power it would otherwise. Heat dissipation is minimized if
                    switching is fast
                    > enough as the waveform spends relatively little time transitioning
                    through
                    > the lnear regions and most of its time either saturated or cut
                    off. It's the
                    > same reason that switching power supplies are so much more
                    efficient.
                  • Roy J. Tellason
                    ... What?
                    Message 9 of 20 , May 6, 2004
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                      On Thursday 06 May 2004 02:08 pm, Stefan Trethan wrote:
                      > > It's the
                      > > same reason that switching power supplies are so much more efficient.
                      >
                      > doubt that.

                      What?
                    • Roy J. Tellason
                      ... Can t compare *what* to a 60 Hz transformer?
                      Message 10 of 20 , May 6, 2004
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                        On Thursday 06 May 2004 02:11 pm, Stefan Trethan wrote:
                        > On Thu, 06 May 2004 20:08:35 +0200, Stefan Trethan <stefan_trethan@...>
                        >
                        > wrote:
                        > >> It's the
                        > >> same reason that switching power supplies are so much more efficient.
                        > >
                        > > doubt that.
                        > >
                        > > ST
                        >
                        > sorry, did rethink it... if you compare switching supply to linear supply
                        > then it is of course true. but you can't compare it to e.g. a 60hz
                        > transformer.

                        Can't compare *what* to a 60 Hz transformer?
                      • Roy J. Tellason
                        ... Actually, voltage isn t what moves, _current_ is. And while radio waves may propagate at the speed of light, current doesn t, necessarily. See
                        Message 11 of 20 , May 6, 2004
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                          On Thursday 06 May 2004 02:16 pm, Phil wrote:

                          > By the way, "slowing down voltage" is a non-sequiter unless we are
                          > talking about changing the speed of light. But the speed of light
                          > isn't just a good idea, ITS THE LAW. sorry, couldn't resist.

                          Actually, "voltage" isn't what moves, _current_ is. And while radio waves
                          may propagate at the speed of light, current doesn't, necessarily. See
                          "velocity factor" when specifying coax cables, for example. :-)
                        • Steve
                          ... t-masspec.shtml 8.6Kg/Km http://www.rfcafe.com/references/electrical/wire_cu.htm So 8.6g/m (I love the metric system) divided by 1.06x10^-22 g/atom = about
                          Message 12 of 20 , May 6, 2004
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                            --- In Electronics_101@yahoogroups.com, "Roy J. Tellason"
                            <rtellason@b...> wrote:
                            > On Thursday 06 May 2004 02:16 pm, Phil wrote:
                            >
                            > > By the way, "slowing down voltage" is a non-sequiter unless we are
                            > > talking about changing the speed of light. But the speed of light
                            > > isn't just a good idea, ITS THE LAW. sorry, couldn't resist.
                            >
                            > Actually, "voltage" isn't what moves, _current_ is. And while
                            radio waves
                            > may propagate at the speed of light, current doesn't, necessarily.
                            See
                            > "velocity factor" when specifying coax cables, for example. :-)

                            And even the velocity factor is not about electrons moving.

                            Think about it- you turn on the tap, and water comes out instantly.
                            Yet it does not travel from the city pressurized tanks at the speed of
                            light, not even at the speed of sound. In fact it travels more like a
                            couple of miles per hour.

                            In other words, you stuff some electrons in one end of a wire, and the
                            electrons that come out the other end are not the same electrons. They
                            are the electrons that were already at that end of the wire.

                            How many electrons in a coulomb? An amp is one coulomb per second.

                            From Wikipedia: One coulomb is 6.24×10^18 electrons.

                            How many atoms in 1 meter of 16 gauge copper wire?

                            1.06×10^-22 g per copper atom
                            http://antoine.frostburg.edu/chem/senese/101/atoms/faq/atomic-masses-withou=
                            t-masspec.shtml

                            8.6Kg/Km
                            http://www.rfcafe.com/references/electrical/wire_cu.htm

                            So 8.6g/m (I love the metric system) divided by 1.06x10^-22 g/atom =
                            about 8.11x10^22 atoms. Since there is one electron in the outer shell
                            of a copper atom, that's an equal number of electrons.

                            So without taking into account the considerable randomness of an
                            electrons walk, how long do we have to push 1 amp of current through a
                            1 meter 16 gauge wire before the electrons we put in start coming out?

                            8.11x10^22 electrons in 1 meter of 16 gauge wire / 6.24x10^18
                            electrons per second = about 13,000 seconds or 217 minutes or just
                            over 3 1/2 hours.

                            So why slow it down? ;') It's a wonder electricity gets -anything- done!

                            Alien Steve
                          • Roy J. Tellason
                            ... Unless you subscribe to the theory that all electrons are the same one, traveling the entire length of the time axis of the space-time continuum multiple
                            Message 13 of 20 , May 6, 2004
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                              On Thursday 06 May 2004 04:30 pm, Steve wrote:

                              > > See "velocity factor" when specifying coax cables, for example. :-)

                              > And even the velocity factor is not about electrons moving.
                              >
                              > Think about it- you turn on the tap, and water comes out instantly.
                              > Yet it does not travel from the city pressurized tanks at the speed of
                              > light, not even at the speed of sound. In fact it travels more like a
                              > couple of miles per hour.
                              >
                              > In other words, you stuff some electrons in one end of a wire, and the
                              > electrons that come out the other end are not the same electrons. They
                              > are the electrons that were already at that end of the wire.

                              Unless you subscribe to the theory that all electrons are the same one,
                              traveling the entire length of the time axis of the space-time continuum
                              multiple times and taking different paths each time...

                              Positrons would be the ones going backwards. :-)
                            • Phil
                              sheesh, ok, ok, all you physicists.... my point was that slowing voltage is a non sequiter. pick at that one now. I love the smell of quibbling in the
                              Message 14 of 20 , May 6, 2004
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                                sheesh, ok, ok, all you physicists.... my point was that slowing
                                voltage is a non sequiter. pick at that one now.

                                I love the smell of quibbling in the morning, smells like...
                                <censored>
                              • JanRwl@AOL.COM
                                In a message dated 5/6/2004 11:14:21 AM Central Standard Time, rowanbeef@yahoo.com writes: Why couldn t someone just use a resistor to drop the voltage?
                                Message 15 of 20 , May 6, 2004
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                                  In a message dated 5/6/2004 11:14:21 AM Central Standard Time, rowanbeef@... writes:
                                  Why couldn't someone just use a resistor to drop the voltage? 
                                  Wouldn't that be the simplest way?  Would it get too hot dropping
                                  that much voltage?  Is it not the most reliable way to get a constant
                                  output?
                                  If the LOAD is steady (not changing), the resistor would be the simple/cheapest way.  But if the load VARIES, some kind of "linear regulator" such as the LM-317, etc., would be indicated. 
                                • Stefan Trethan
                                  ... Can t compare a transformer (maybe with bride and cap) to a switching power supply. because the switching supply offers regulated voltage instantly, while
                                  Message 16 of 20 , May 7, 2004
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                                    >
                                    > Can't compare *what* to a 60 Hz transformer?
                                    >

                                    Can't compare a transformer (maybe with bride and cap)
                                    to a switching power supply. because the switching supply offers
                                    regulated voltage instantly, while the transformer supply needs a regulator
                                    which could be less efficient.

                                    ST
                                  • Stefan Trethan
                                    ... Actually not the current moves, the charge carriers move. (the voltage moves the same as the current, imagine a wire where you apply a voltage, if you
                                    Message 17 of 20 , May 7, 2004
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                                      > Actually, "voltage" isn't what moves, _current_ is. And while radio
                                      > waves
                                      > may propagate at the speed of light, current doesn't, necessarily. See
                                      > "velocity factor" when specifying coax cables, for example. :-)
                                      >

                                      Actually not the current moves, the charge carriers move.
                                      (the voltage moves the same as the current,
                                      imagine a wire where you apply a voltage, if you measure the voltage
                                      at the output in X seconds you will measure it in the middle of the wire
                                      in X/2 seconds. see, the voltage has "moved".).

                                      the term "current" describes the "rate of movement" and voltage describes
                                      the "difference in potential". it are attributes of points, or between 2
                                      points.
                                      they don't move.

                                      Imagine a transparent hose, you fill green liquid in at one end.
                                      the liquid will move with a certain velocity.
                                      the "current" beeing the flow rate is tied to a point along the length of
                                      the hose.
                                      the "voltage" beeing the "is it green or not" is also a parameter of a
                                      point.

                                      What moves are the electrons (in metals).
                                      There are two different speeds, one is the speed information travels (only
                                      a bit under
                                      the speed of light, depending on cable, estimate with 30cm/ns) and the
                                      other
                                      is the speed the electrons move. we call it "drift speed" here, not sure
                                      'bout the
                                      english terms. i think i once calculated it at a few cm per second.

                                      I agree slowing down the voltage is not valid, slowing down the current
                                      would
                                      theoretically be valid, as "decreasing dQ/dt", but people would look at
                                      you strange.

                                      ST
                                    • Steve
                                      ... example. :-) ... one, ... continuum ... Which would explain why they repel each other, cause if they ever touch they will combine into a wierd bloody
                                      Message 18 of 20 , May 7, 2004
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                                        --- In Electronics_101@yahoogroups.com, "Roy J. Tellason"
                                        <rtellason@b...> wrote:
                                        > On Thursday 06 May 2004 04:30 pm, Steve wrote:
                                        >
                                        > > > See "velocity factor" when specifying coax cables, for
                                        example. :-)
                                        >
                                        > > And even the velocity factor is not about electrons moving.
                                        > >
                                        > > Think about it- you turn on the tap, and water comes out instantly.
                                        > > Yet it does not travel from the city pressurized tanks at the speed of
                                        > > light, not even at the speed of sound. In fact it travels more like a
                                        > > couple of miles per hour.
                                        > >
                                        > > In other words, you stuff some electrons in one end of a wire, and the
                                        > > electrons that come out the other end are not the same electrons. They
                                        > > are the electrons that were already at that end of the wire.
                                        >
                                        > Unless you subscribe to the theory that all electrons are the same
                                        one,
                                        > traveling the entire length of the time axis of the space-time
                                        continuum
                                        > multiple times and taking different paths each time...
                                        >
                                        > Positrons would be the ones going backwards. :-)

                                        Which would explain why they repel each other, 'cause if they ever
                                        touch they will combine into a wierd bloody blob on the floor going
                                        "oooaaawwoooowaaawwoooo..." and then disappear!

                                        Seriously... I recall that theory, haven't heard any mention of it for
                                        quite a while. Don't know how or if it is supposed to tie into brane
                                        theory and string theory.

                                        Alien Steve
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