I'm having trouble tracking down typical Capacitor ESR values for Aluminum and Tantalum electrolytics.
Can someone point me to a page?
Or some rules of thumb I can use in simulations?
Thanks!
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |
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| 1962 | I love to cook with wine. Sometimes I even put it in the food.
Thanks, At least that gives me some ball-park numbers.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Capacitor manufacturers no longer like to state ESR, because it depends on the frequency of interest. As you may have noticed, they do state Dissipation Factor (DF) instead. I had to do some poking around a few weeks ago to find the secret formula to convert DF into ESR, and here's what I learned.
DF/(2*pi*frequency*capacitance) = R
Assume a data sheet DF of .05% And assume you are doing some work at, say, 1kHz, and the capacitance is, say, 20uF.
So in this instance:
0.0005/(2*3.1416*1000*.000020 = 3.97 milliohms
--
Mike "Rocket J Squirrel" Elliott
71 VW Type 2 -- the Wonderbus (AKA the Saunabus in summer)
Wouldn't that mean you need DF given at a specific frequency so that you can work back to ESR (which should(?) be fairly constant)?
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
At 0Hz, the ESR of a capacitor will be darn high. It drops as one goes up in frequency until inductance takes over.
When you do find specs for ESR in capacitor data sheets, they specify at which frequency (usually 120Hz in the US) they are providing the ESR for.
According to
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Equivalent Series Resistance (ESR)
It's the sum of all the internal resistances of a capacitor measured in Ohms. It includes:
- Resistance due to aluminum oxide thickness
- Resistance due to electrolyte / spacer combination
- Resistance due to materials (Foil length; Tabbing; Lead wires; Ohmic contact resistance)
The lower the ESR the higher the current carrying ability the capacitor will have. The amount of heat generated by ripple current depends upon the ESR of the capacitor.
ESR is both frequency and temperature dependent, increasing either will cause a reduction in ESR. The ESR is an important parameter in calculating life expectancy as the power dissipation (internally generated heat) is directly proportional to its value.
--
Mike "Rocket J Squirrel" Elliott
71 VW Type 2 -- the Wonderbus (AKA the Saunabus in summer)
I think dissipation factor includes several factors, one of which is ESR. The bigger factor at higher frequencies is a fairly constant per cycle loss. Your formula looks like it is interpreting those per cycle losses as ESR. Not very useful, I suspect.
, their AO-CAP alum. caps have ESR@100k ~25-15 mohm. For Tants see the 'Solid Tant Chip Performance characteristics'. Here is where DF=ESR/Xc=2xPIxFxCxR
You may be right. My formula was provided by the engineer at ASC, and I've also seen it on some online sites as well. I'll bet that the formula is useful for line-frequency based power supplies, though.
--
Mike "Rocket J Squirrel" Elliott
71 VW Type 2 -- the Wonderbus (AKA the Saunabus in summer)
Jim, if you tell me what style capacitor (el cheapo, low-esr, ...), I might be able to measure the Z on our network analyzer. Z data varies quite a bit depending on capacitor construction. ESR can vary quite a bit over frequency, perhaps over 100 to 1 for some ceramic caps (as reported by AVX's SpiCap program.
FYI, AVX has good data on their ceramic and tantalum caps. Aloha, Mark
I've tried some of these AO caps, the A700 series, and one nice thing, unlike alot of tantalums and some niobium, is they don't go up in flames....ran a 4V version to 14V and held it there, and then back down, it nearly recovered all its original characteristics.
Au contraire- if you look at that so-called formula it is the definition of DF which is the cotangent of the impedance angle of a simple series R-C equivalent circuit. The DF being small allows the identity between ratio and tangent function. The small in-phase component of voltage with current is exactly that fraction of the VA producing dissipated versus stored energy per cycle and is the equivalent resistance at the measurement conditions, where resistance is abstracted from being just a chunk material of finite conductivity to an energy-to-heat conversion element. It will be non-linear, a functional dependence on temperature, frequency, and signal level.
If you want to interpret all losses as if they were a result of an actual series resistance, and the total losses are low, the formula is fine. If you want to know what the parallel losses, the series losses and the hysterisis losses are, it is not much use. I think the best way to measure the actual series resistance is to subject the cap to its series resonant frequency and and measure its impedance.
Are you saying that the best model would be a series R-L-C evaluated at resonance?
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
LTspice's capacitor database just uses 1 R and 1 C as an quick and effective approximation. But if you use 2 R's and C's, you can model the phase angle of the impedance correct within a few degrees over many decades of freq. Three 3 R's and 3 C's should let you model more accurately than you can measure with any component analyzer I know of.
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