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Old 20th December 2011, 06:28 AM   #291
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Quote:
Originally Posted by gootee View Post
Cornell Dubilier Electronics Java Applet tells it all
Good find; thanks for sharing. It's the other end of the cap spectrum but for MLCCs I usually use TDK's Component Characteristics Viewer; other vendors have similar tools but TDK's UI is lower friction than most.

Just about all my design is with radial or surface mount parts, so that explains it. Pretty much never look at caps that would mount off board.
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Old 20th December 2011, 11:36 PM   #292
gootee is offline gootee  United States
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Quote:
Originally Posted by magnoman View Post
Benb

I have also found similar results. The RC acts as a snubber (if you can measure the ringing frequency then you can just add enough capacitance to start decreasing the frequency, or preferably halve it, then a series R of the same resonant impedance value).
To tie this back to the power plane issue you still need a low inductance connection to the pure C and so the power planes again allow these RC's to be located some distance away and still be effective.

Thanks
-Antonio

PRACTICAL SNUBBER AND TERMINATION DESIGN

Below is a pretty slick and practical way to determine parasitic capacitance and/or inductance, and the characteristic impedance and optimal damping or termination resistance (and snubber capacitance) needed when ringing or reflections (as the case may be) are present.This is a very simple method for determining the capacitance and the inductance that are causing a resonance in a circuit or a transmission line or PCB trace, which also gives the characteristic impedance for the resonant circuit, which is everything needed in order to know how to damp it, optimally. (I refer to the C and L as parasitic. But this method and the math may be used when either one, or both, or neither is parasitic, in case an installed inductor and/or capacitor are involved.)

This assumes that there is a ringing condition, already, such as might occur on a digital buss or a transmission line or PCB trace, or in a switch-mode power supply or even an AC-to-DC transformer/rectifier circuit, and in many other types of circuits. (If you don't have ringing and just want to determine some of these parameters, I guess maybe you could try hitting your circuit with a pulse train and decrease the rise and fall times until it rings.)

1. Measure the frequency of the resonance or ringing, using an
oscilloscope (or a circuit simulator, if you've modeled the parasitics well).

2. Add a shunt capacitor and adjust the value of this capacitor until the frequency of the ringing is reduced by a factor of two. I've left out the math but the value of this resulting capacitor will be three times (3X) the value of the parasitic capacitance that is creating the resonance.

3. Because the parasitic capacitance is now known, the parasitic inductance can be determined using the formula:

L = 1 / [(2 Pi F) C]

where F = (original) resonant frequency and C = parasitic capacitance.

4. Now that both the parasitic capacitance and inductance are known, the
characteristic impedance of the resonant circuit can be determined using the following formula:

Z = √(L/C)

where L = parasitic inductance and C = parasitic capacitance.

5. The resistor value used for the terminator or for the RC snubber circuit should be equal to Z, the value of the characteristic impedance, and the capacitor, if used, should be sized between four and ten times the parasitic capacitance. The use of larger (than 4X) capacitors slightly reduces the voltage overshoot at the expense of greater power dissipation in the resistor.

NOTE: The resistor, alone, is all that is needed to prevent or damp-out the ringing (or reflections, as the case may be). But if power dissipation in the R would then be too high, a C is added in series with the R, so that only the unwanted frequencies cause currents in the resistor. (And that, boys and girls, is the only reason there's a capacitor in a snubber.)

Cheers,

Tom

Last edited by gootee; 21st December 2011 at 12:05 AM.
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Old 21st December 2011, 12:51 AM   #293
gootee is offline gootee  United States
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This extended ASCII table seems correct:

ASCII Table; ASCII extended character sets; IBM PC

I found some interesting stuff at the Unicode links for some of the characters.

And here is a compacted version (hover over characters for info):

ASCII Table

-----------

Oh my!! The following link seems amazingly complete, regarding "character code" issues! This is The Mother Lode!

http://www.cs.tut.fi/~jkorpela/chars.html


Cheers,

Tom

Last edited by gootee; 21st December 2011 at 01:02 AM.
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Old 21st December 2011, 01:44 AM   #294
gootee is offline gootee  United States
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How to Easily Use Special Characters with Windows

OK! I FINALLY found "The Easy Way" to post any available character you want, with Windows!

e.g. ∂∆≈

Taj said, "FYI: Windows users can use the built-in "Character Map" software (Start menu> Accessories> System Tools) to select and paste the proper Unicode glyphs into this forum."

On my XP machine, I have to do the following:

Start → All Programs → Accessories → System Tools → Character Map

(Notice the nice arrows... :-)

Then I can simply click on the characters in a table to see them enlarged, click Select to add each one to my list, and click Copy to copy my list to the clipboard.

Ω ≠ ∞

small Pi: π
capital Pi: Π

Not too nice-looking...

But wait! That was the Arial version (i.e. no serifs, since Arial is a "sans serif" font)!

Π π

⅞ ∑ ∏ ∫ ∕ − ≤ ≥ ₪


That's more like it! (But I also had to select and wrap the Pi characters with "Times New Roman" in the Advanced post editor, here.)

And below is the second line without the Times Roman. But it was taken from the "Mathematical Symbols" grouping, after I selected "Unicode Subrange" in the "Group By" selection, to see the table displayed by groupings (and the thing that looks like PI is listed as "n-ary product" in the "Mathematical Operators" sub-grouping):

⅞ ∑ ∏ ∫ ∕ − ≤ ≥ ₪

Larger, in the default font:

⅞ ∑ ∏ ∫ ∕ − ≤ ≥ ₪


Cheers,

Tom

Last edited by gootee; 21st December 2011 at 02:12 AM.
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Old 21st December 2011, 02:23 AM   #295
benb is offline benb  United States
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This brings up yet another rant from me, and confusion among a lot of vBulletin posters, especially on the writing board I frequent. People expect, somewhat reasonably, that they can do formatting in Microsoft Word or another text editor/word processor using different fonts and font sizes, and variations such a bold and italic, and that they can copy/paste it into an online message board like this and have it come out right. But the formatting codes are all different and the "clipboard" doesn't know it should convert things when pasting into such a message board editing window, and even if it did there are incompatibilities such as limited number of font sizes that would make the result at best not quite WYSIWIG.

I remember when the IBM PC came out, the (monochrome and CGA) display was "yet another" 8-bit extension to the original 7-bit ASCII character set, after other computers such as the Apple ][, other early microcomputers and innumerable terminals used all different sets for the "upper" 128 display characters. But of course due to the popularity of the PC, the IBM PC's set became the de-facto standard, and eventually part of the "official" ISO character set standard(s). And yes, the "ALT codes" were part of the original IBM PC's BIOS ROM.

There must be some "parallel" to the main discussion here, but offhand I can't think of what it would be.
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Old 21st December 2011, 03:03 AM   #296
gootee is offline gootee  United States
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(Sorry to get off-topic, for the moment.)

Yeah, tell me about it. I used to write C code for those things, including a bunch of different character-based terminal types under Unix and also made it all portable across Xenix, and Linux, and DOS/Netware, Windows 3.1, etc. I remember that the first source-code function I wrote was something to "put the cursor at screen position x, y", and I built from there. I used the box-drawing characters extensively, to make nice non-scrolling data-entry forms and also to allow drawing general-shaped outlines by entering length & direction pairs (don't ask), and after finally getting that all sorted I also had to figure out how to make it portable across many different printers (remember the Okidata 192?), for printing forms with box-character drawings etc and for PrtScr (which, I remember, was "interesting" on the Wyse 60 terminal, because it involved the code for Ctrl-S, which stopped everything; but I eventually figured it out). When HP's LaserJet II came out, I also wrote a preprocessor for the Unix "nroff" document-formatting utility, so it could use the two fonts I had for my LJ II and actually get all of the font sizing and spacings and margins and tables of contents and page numbering (etc!) and everything done properly. What a pain.

L = 1 ∕ (C(2πf))

HOW can I make a line with leading whitespaces, when posting here?

Cheers,

Tom

Last edited by gootee; 21st December 2011 at 03:16 AM.
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Old 21st December 2011, 03:42 AM   #297
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In response to damping the resonance of parallel connected caps. I look at it as pi filter
wich can be damped by either introducing serial resistance or parallel resistance or a combination of it. If parallel resistance is used a serial cap must be used to avoid the otherwise obviously resulting loss in dc power. This serial cap has to be at least 10 times (better 20 times) bigger than the cap at the output of the pi filter. Also it has to be remembered that any small valtage changes at the input of the pi filter will be transformed into much higher amplitude at the output.
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Old 21st December 2011, 03:59 AM   #298
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If it is really necessary to use a "parallel" cap it is best to minimize the serial inductance to a point where the losses are sufficient to keep the circuit-Q at or below 0.5 wich most certainly almost always should be possible. Anyway, if I see 0.1uF caps it makes me wonder why it is 0.1uF and not some other value? Has the designer given it much thaught and was he aware of all the the things that should be considered? I find it hard to believe that the rigth value for a parallel cap turns out to be just 0.1uF in each and every case I see those caps applied too.
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Old 23rd December 2011, 06:16 PM   #299
gootee is offline gootee  United States
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What is the significance of phase angle or group delay, in a plot of the impedance seen by the amplifier power/gnd pins?
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Old 23rd December 2011, 08:50 PM   #300
gootee is offline gootee  United States
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Here's one that claims to prove that multiple decoupling/bypass values are better than multiple caps of the same value (and that fewer caps can be used if they have higher ESR):

http://www.n4iqt.com/BillRiley/multi...ypass-caps.pdf

Last edited by gootee; 23rd December 2011 at 08:54 PM.
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