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Re: [Electronics_101] what does this capacitor do (Alan) ?

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  • John Popelish
    Keep in mind that current passing through resistors also generates white noise voltage, so that little cap also low pass filters that signal . One thing the
    Message 1 of 13 , Apr 11, 2013
      Keep in mind that current passing through resistors also generates white
      noise voltage, so that little cap also low pass filters that 'signal'. One
      thing the video did not mention is that, in some single supply
      applications, the positive rail is closer to acting as a signal common (for
      instance, when the positive rail is what the enclosure is connected to)
      than the negative rail is. In those cases, the capacitor would go to the
      positive rail.

      --
      Regards,

      John Popelish


      On Wed, Apr 10, 2013 at 7:21 PM, jongkung01 <jongkung01@...> wrote:

      > Hi Alan (and anybody else who can chime in),
      >
      >
      > I was enjoying your video on Op-Amp and split PS (and other videos):
      >
      > http://www.youtube.com/watch?v=MtccB9K09ck
      >
      > At around 1:54 minute mark, you show a capacitor to ground on the input of
      > non-inverting input. You say it decouples it.
      >
      > I don't get it. I know capacitors in that configuration will pass AC to
      > ground. But what AC ??
      >
      > And the capacitor has no marking / typical value. What would be a good
      > range of typical values would work?
      >
      > =====
      >
      > I am basically a hobbyist and not dealing with anything into Mhz range.
      > Does it matter if the circuit (op-amp) is used in <<Mhz configuration (to
      > not have this capacitor) ??
      >
      > Would this be called by-pass capacitor or decoupling capacitor ?
      >
      > ======
      >
      > I often see in some diagram for 555 circuits a capacitor for PIN 5 (if I
      > remember) - but in practice they often skip it. Does it serve the same
      > function ? I think I understand the reason for capacitor on Pin 5 (when
      > not used to control freq), but I still don't see why a capacitor on + input
      > leg of Op-Amp.
      >
      >
      > Thanks in Advance,
      >
      >
      > Jong
      >
      >
      >
      >
      > ------------------------------------
      >
      > Please trim excess when replyingYahoo! Groups Links
      >
      >
      >
      >


      [Non-text portions of this message have been removed]
    • jong kung
      John, et al, Thanks... There s so many things they gloss over in EE textbooks. I always see these capacitors, and I KNOW they are suppose to make output
      Message 2 of 13 , Apr 11, 2013
        John, et al,


        Thanks...

        There's so many things they gloss over in EE textbooks. I always see these capacitors, and I KNOW they are suppose to make output signal cleaner - but never understood why or how. They are ALL making sense now.

        I love these moments of Ah-Ha!!! Decades of wondering all snaps into place in one moment.

        ======

        > One
        > thing the video did not mention is that, in some single
        > supply
        > applications, the positive rail is closer to acting as a
        > signal common (for
        > instance, when the positive rail is what the enclosure is
        > connected to)
        > than the negative rail is. In those cases, the
        > capacitor would go to the
        > positive rail.

        Oh - thanks for that too. I probably saw that and never even knew that cap to the positive rail could be for the same reason.


        Jong




        --- On Thu, 4/11/13, John Popelish <jpopelish@...> wrote:

        > From: John Popelish <jpopelish@...>
        > Subject: Re: [Electronics_101] what does this capacitor do (Alan) ?
        > To: Electronics_101@yahoogroups.com
        > Date: Thursday, April 11, 2013, 3:12 AM
        > Keep in mind that current passing
        > through resistors also generates white
        > noise voltage, so that little cap also low pass filters that
        > 'signal'.  One
        > thing the video did not mention is that, in some single
        > supply
        > applications, the positive rail is closer to acting as a
        > signal common (for
        > instance, when the positive rail is what the enclosure is
        > connected to)
        > than the negative rail is.  In those cases, the
        > capacitor would go to the
        > positive rail.
        >
        > --
        > Regards,
        >
        > John Popelish
        >
      • Derek
        The capacitor is to help stabilize the non-inverting input signal. With the voltage divider, it is a virtual ground since there is impedance to the ground
        Message 3 of 13 , Apr 11, 2013
          The capacitor is to help stabilize the non-inverting input signal. With
          the voltage divider, it is a virtual ground since there is impedance to
          the ground reference. Value should be between 0.1 and 1.0 uF as stated
          earlier for noise. Another option is to just use a single resistor to
          ground. Issue with two resistors in the video is that the resistors are
          not all equal - yes, it may be spec'd as 10k each, but in reality there
          is a slight difference.

          I recently designed a circuit where I was operating off a single supply
          and needed to use inverting opamps to flip the signal and flip it back
          due to an active filter circuit. Using two separate resistors, though
          referenced to each opamp is the same, still did not get me the same as
          the input; there was a significant offset from the input. Instead of two
          resistors, I used a resistor divider which had a spec of percent
          difference between the two internal resistors. This had much better result.

          Another set of caps one should use near opamps is the supply rail filter
          caps. A switch-mode supply does inject noise into a signal through the
          supplies. Thus, filtering at the opamp on the supply rails with a 0.1 to
          1 uF cap helps deal with large gain circuits.

          Derek Koonce
          DDK Interactive Consulting Services

          On 4/10/2013 4:21 PM, jongkung01 wrote:
          >
          > Hi Alan (and anybody else who can chime in),
          >
          > I was enjoying your video on Op-Amp and split PS (and other videos):
          >
          > http://www.youtube.com/watch?v=MtccB9K09ck
          >
          > At around 1:54 minute mark, you show a capacitor to ground on the
          > input of non-inverting input. You say it decouples it.
          >
          > I don't get it. I know capacitors in that configuration will pass AC
          > to ground. But what AC ??
          >
          > And the capacitor has no marking / typical value. What would be a good
          > range of typical values would work?
          >
          > =====
          >
          > I am basically a hobbyist and not dealing with anything into Mhz
          > range. Does it matter if the circuit (op-amp) is used in <<Mhz
          > configuration (to not have this capacitor) ??
          >
          > Would this be called by-pass capacitor or decoupling capacitor ?
          >
          > ======
          >
          > I often see in some diagram for 555 circuits a capacitor for PIN 5 (if
          > I remember) - but in practice they often skip it. Does it serve the
          > same function ? I think I understand the reason for capacitor on Pin 5
          > (when not used to control freq), but I still don't see why a capacitor
          > on + input leg of Op-Amp.
          >
          > Thanks in Advance,
          >
          > Jong
          >
          >



          [Non-text portions of this message have been removed]
        • Andy
          ... I rather doubt it. What s unimportant in one usage, may be critical in another. What freq. range is pretty obvious though. If it is within the frequency
          Message 4 of 13 , Apr 11, 2013
            > Is there an approx / general rule on at what amplification and freq the noise might be important?

            I rather doubt it. What's unimportant in one usage, may be critical in another.

            What freq. range is pretty obvious though. If it is within the
            frequency range of your circuits, and/or your signals, then it is
            worth considering.

            Andy
          • AlienRelics
            ... Here is one: you took a TO-220 transistor off of a heat sink to replace it. You are about to replace it, but you look down at a pile with a bolt, flat
            Message 5 of 13 , Apr 12, 2013
              --- In Electronics_101@yahoogroups.com, jong kung <jongkung01@...> wrote:
              >
              > John, et al,
              >
              >
              > Thanks...
              >
              > There's so many things they gloss over in EE textbooks. I always see these capacitors, and I KNOW they are suppose to make output signal cleaner - but never understood why or how. They are ALL making sense now.
              >
              > I love these moments of Ah-Ha!!! Decades of wondering all snaps into place in one moment.
              >

              Here is one: you took a TO-220 transistor off of a heat sink to replace it. You are about to replace it, but you look down at a pile with a bolt, flat washer, and split-ring washer... in what order do you reassemble the bolt and washers?

              I found this information about 20 years ago in a machinist's manual, detailing what purpose a split-ring washer is for and why you always use it with a flat washer. It was the opposite of what everyone around me was saying, including experienced EEs and teachers.

              And I recently got into a disagreement with an EE about this very subject.

              Steve Greenfield AE7HD
            • William Myrick
              Steve please share that information,why it is used with, us. Derward Myrick KD5WWI ... From: AlienRelics Sent: Apr 12, 2013 8:02 AM To:
              Message 6 of 13 , Apr 12, 2013
                Steve please share that information,why it is used with, us.

                Derward Myrick KD5WWI

                -----Original Message-----

                From: AlienRelics

                Sent: Apr 12, 2013 8:02 AM

                To: Electronics_101@yahoogroups.com

                Subject: [Electronics_101] Hidden information Re: what does this capacitor do (Alan) ?
















                .
              • jong kung
                SG, ... I usually just put thing back in the order I found so I never gave this much thought. But here s my GUESS. (1) Regular washer is often used to SPREAD
                Message 7 of 13 , Apr 12, 2013
                  SG,


                  > Here is one: you took a TO-220 transistor off of a heat sink
                  > to replace it. You are about to replace it, but you look
                  > down at a pile with a bolt, flat washer, and split-ring
                  > washer... in what order do you reassemble the bolt and
                  > washers?


                  I usually just put thing back in the order I found so I never gave this much thought. But here's my GUESS.

                  (1) Regular washer is often used to SPREAD the pressure of the bolt or nut (head) to a wider area around the hole.

                  (2) The split washer is used to create a slight spring effect to prevent it from coming loose.

                  So my guess is to put the split ring washer in between the head of the bolt (or nut) and the regular washer. The regular washer goes up against the hole (pcb, etc.) to spread the pressure evenly - with or without the split washer (the spring).

                  =====

                  I'm guessing that some people think that the EDGE of the split digs into the surface of the PCB and the head of the bolt (or nut) and the friction is what prevents the fastener from coming loose. But that is not true. It is so that even if the faster is NOT completely tight, there's some pressure that prevents the fastener from just spinning loose.


                  Jong
                • John Popelish
                  You might think that more capacitance is simply better, because it increases the low pass filter attenuation for any noise. But this must be weighed against
                  Message 8 of 13 , Apr 12, 2013
                    You might think that more capacitance is simply better, because it
                    increases the low pass filter attenuation for any noise. But this must be
                    weighed against the time it takes for the bias point to stabilize, after
                    power is turned on, of the effect of having that charged capacitor dumping
                    charge into the input pin, after the power supply has been turned off.
                    Sometimes the resistor to the far rail in the bias divider needs to be
                    paralleled with a reverse biased diode, to drain that capacitor charge back
                    to the rail, as the supply voltage falls, to prevent damage to a sensitive
                    input.


                    On Fri, Apr 12, 2013 at 12:58 AM, Andy <ai.egrps@...> wrote:

                    > > Is there an approx / general rule on at what amplification and freq the
                    > noise might be important?
                    >
                    > I rather doubt it. What's unimportant in one usage, may be critical in
                    > another.
                    >
                    > What freq. range is pretty obvious though. If it is within the
                    > frequency range of your circuits, and/or your signals, then it is
                    > worth considering.
                    >
                    > Andy
                    >
                    >
                    > ------------------------------------
                    >
                    > Please trim excess when replyingYahoo! Groups Links
                    >
                    >
                    >
                    >


                    [Non-text portions of this message have been removed]
                  • Willie Pierce
                    It depends I ve seen lock washers used to slightly cut into or gouge a little on a metal surface to make sure it has a clean contact point.... but in general
                    Message 9 of 13 , Apr 12, 2013
                      It depends I've seen lock washers used to slightly cut into or gouge a little on a metal surface to make sure it has a clean contact point....

                      but in general I've always been told it was use to keep pressure on the bolt so it stayed tight.

                      On Apr 12, 2013, at 10:57 AM, John Popelish <jpopelish@...> wrote:

                      > You might think that more capacitance is simply better, because it
                      > increases the low pass filter attenuation for any noise. But this must be
                      > weighed against the time it takes for the bias point to stabilize, after
                      > power is turned on, of the effect of having that charged capacitor dumping
                      > charge into the input pin, after the power supply has been turned off.
                      > Sometimes the resistor to the far rail in the bias divider needs to be
                      > paralleled with a reverse biased diode, to drain that capacitor charge back
                      > to the rail, as the supply voltage falls, to prevent damage to a sensitive
                      > input.
                      >
                      > On Fri, Apr 12, 2013 at 12:58 AM, Andy <ai.egrps@...> wrote:
                      >
                      > > > Is there an approx / general rule on at what amplification and freq the
                      > > noise might be important?
                      > >
                      > > I rather doubt it. What's unimportant in one usage, may be critical in
                      > > another.
                      > >
                      > > What freq. range is pretty obvious though. If it is within the
                      > > frequency range of your circuits, and/or your signals, then it is
                      > > worth considering.
                      > >
                      > > Andy
                      > >
                      > >
                      > > ------------------------------------
                      > >
                      > > Please trim excess when replyingYahoo! Groups Links
                      > >
                      > >
                      > >
                      > >
                      >
                      > [Non-text portions of this message have been removed]
                      >
                      >


                      [Non-text portions of this message have been removed]
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