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Old 25th July 2012, 06:05 AM   #291
gootee is offline gootee  United States
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Quote:
Originally Posted by fas42 View Post
Bit of a thread to digest, so I'll wind up my energy to chomp my way through it later on. At a quick glance, I can see that people get into trouble by ignoring the lead and connections' inductances; this will kill any benefit of bypassing, possibly make it worse, unless it's done precisely where it's needed. Rule of thumb, the smaller the cap the closer it has to be where the HF noise is the actual problem.

In general, ESR is relatively constant over the range that the cap deals with, it's the impedance that starts capacitive, momentarily becomes resistive, and then remains forever inductive, with rising frequency.

Frank
I was going to respectfully disagree, and was going to say the following:

----------------

ESR varies directly with frequency. (It is part of the impedance, too).

DF = TAN(DELTA)@f = 2Pi*f*C*ESR(f)

The tan(delta), or DF (dissipation factor), varies by only about 100%, usually. So we can use that to estimate ESR versus frequency, with

ESR(f) = tan(delta)/(2 Pi f C)

----------------

But then I looked at:

Cornell Dubilier Electronics

which gives something like this:

http://www.diyaudio.com/forums/attac...ps-cdejava.jpg

And so another long-held misconception bites the dust.

Thank you. I just wish I had noticed that, years ago, before it cost me so much extra effort when doing spice modeling and simulation. (But the capacitor spice models from that CDE java applet are coool.)

Cheers,

Tom

P.S.

I'm definitely with you on the inductance issues, and also for demanded current instead of just noise, in a decoupling context.

Last edited by gootee; 25th July 2012 at 06:11 AM.
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Old 25th July 2012, 06:10 AM   #292
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Old 25th July 2012, 06:35 AM   #293
fas42 is offline fas42  Australia
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Quote:
Originally Posted by gootee View Post
I was going to respectfully disagree, and was going to say the following:

----------------



Thank you. I just wish I had noticed that, years ago, before it cost me so much extra effort when doing spice modeling and simulation. (But the capacitor spice models from that CDE java applet are coool.)

Cheers,

Tom

P.S.

I'm definitely with you on the inductance issues, and also for demanded current instead of just noise, in a decoupling context.
And I've just run through some of your "vigorous" input in that thread - we are on the same page!! I've done a lot of thrashing myself using LTspice, that duplicates in many areas the sort of things you were so passionately researching. So, I know exactly why you were beating the drum about current requirements as strongly as you did, and the need to acquire full understanding of all the parasitics in the equation ...

Frank
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Old 25th July 2012, 08:16 AM   #294
forr is offline forr  France
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Quote:
Originally Posted by gootee View Post
Just did a quick LTSpice simulation of a 40V linear power supply with a 14000 uF reservoir cap and an 8 Ohm load, with no ESR and with 0.1 Ohm ESR. The attached ripple voltage plot shows the effect. It's due to ESR.

Click the image to open in full size.

Thanks for this finding. It's worth more investigation.
Is it not a good way to determine the optimal value of the reservoir cap such as the peak in the waveform with ESR does not show up ?
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Old 25th July 2012, 11:35 AM   #295
PChi is offline PChi  United Kingdom
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Quote:
Originally Posted by forr View Post
Click the image to open in full size.

Thanks for this finding. It's worth more investigation.
Is it not a good way to determine the optimal value of the reservoir cap such as the peak in the waveform with ESR does not show up ?
I don't think that it's a good way to determine the optimal value.
If the waveform show significant distortion due to Capacitor ESR it's time to buy a new capacitor.
It's either not a very good capacitor to start with or it has been abused and it's getting near the end of it's life.
In my experience all the reputable manufacturers' capacitors won't show that effect in a typical circuit. I have only seen that sort of waveform with poor quality electrolytic capacitors.
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Old 25th July 2012, 04:28 PM   #296
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Originally Posted by gootee View Post
Thanks for the link.
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Old 25th July 2012, 05:10 PM   #297
forr is offline forr  France
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Quote:
Originally Posted by PChi View Post
I don't think that it's a good way to determine the optimal value.
If the waveform show significant distortion due to Capacitor ESR it's time to buy a new capacitor.
It's either not a very good capacitor to start with or it has been abused and it's getting near the end of it's life.
In my experience all the reputable manufacturers' capacitors won't show that effect in a typical circuit. I have only seen that sort of waveform with poor quality electrolytic capacitors.
Since ten years, I always check all the electrolytic capacitors I use with Cyril Bateman's tan-delta-meter and a capacitor meter. I am not sure many people are equipped with such an apparatus and are so methodical. I hope you are.
Among many I tested, SIC-SAFCO caps always show dependable, reliable, excellent performances.
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Old 25th July 2012, 05:35 PM   #298
MiiB is offline MiiB  Denmark
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There's at lot to learn here....capacitance falls radically with frequency, impedance rises with frequency as the caps turns inductive...hmm...This much more than I had expected. having polypropylene's/ceramic as final reservoirs seems almost mandatory..what is superb spec's worth, if there's no current to deliver.
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Old 25th July 2012, 05:46 PM   #299
PChi is offline PChi  United Kingdom
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Quote:
Originally Posted by forr View Post
Since ten years, I always check all the electrolytic capacitors I use with Cyril Bateman's tan-delta-meter and a capacitor meter. I am not sure many people are equipped with such an apparatus and are so methodical. I hope you are.
Among many I tested, SIC-SAFCO caps always show dependable, reliable, excellent performances.
I don't have Cyril Bateman's tan-delta-meter and I haven't been so methodical.
I was commenting on experience, OK many years ago, when only LCR electrolytic capacitors had significant ESR for a Linear simple rectified power supply though they were cheap.
The Nippon Chemi-con capacitors that were generally used had a low enough ESR that the effect on the wave form was largely absent.
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Old 25th July 2012, 06:20 PM   #300
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Hi guys replace your onboard caps with these caps http://www.diyaudio.com/forums/solid...ml#post3102253
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