Capacitor esr and impeadance?

Nothing? They give you the DF / tan delta, which lets you calculate the Q or esr at low frequencies. They give you the high-frequency ripple-current rating, which is the most important number for switching supplies, etc., and they give you the esr at 100kHz. If you measure these caps on an expensive impedance meter, you'll find a low-frequency Q, which probably never exceeds 200 or so, declining as 25 to 50kHz is approached, above which the cap is better described as a capacitance with a fixed series resistance. That's the esr value they give you. BTW, the values are pretty good for electrolytic caps.

Hello Hammy,

Your datasheet says 0.017 Ohm at 100 kHz. An ideal 1500uF capacitor should have an impedance of 1.1 mOhm. So the excess impedance is caused by inductance and/or resistance.

When it is inductance it would be 27nH. Self inductance of the capacitor is almost independent of temperature, so you can be sure that at low temperature, the impedance is caused by a resistive (=ESR) effect.

If you really want to know it at 20 degrees (or higher), you can measure it by injecting a sine wave signal and measure the voltage across the capacitor, and the current via a series resistor. Based on the phase between I and U you can determine the real component (=ESR) of the impedance. When you inject from a relative high impedance source, you do not need the current sensing resistor (as the current is determined by the source impedance).

When you prefer a time domain approach, you can apply a step (square wave?).

Note that at low temperature and after some years ESR will increase. You can also see this from the 200% increase of dissipation factor after high temp test.

Using DF values for 120 Hz is not good to estimate ESR at high frequency. This is because of the conduction process in electrolytes is strongly frequency dependent.

Best regards,

Wim PA3DJS

Sure they do. In fact, they give it to you twice! -- Once in the "impedance" columns, and secondly via the loss tangent. The impedance columns are specified at 100kHz, and if you run through the numbers, you'll see that while an ideal 1500uF capacitor at 100kHz would have an impedance of about a milliohm, you're told that in actuality it'll be around 17 milliohms at 20C, so you can assume that the vast bulk of that is a loss resistance (say, 16 milliohms).

As for loss tangent... see here for a discussion:

Perhaps someone who has more experience here can comment on the discrepancy. :-)

---Joel

The loss tangent can be composed of both series and shunt losses. This circuit...

----------+---------+ | | C1 C2 | | | | R1 R2 | | | | | |

----------+---------+

can have a very low apparent ESR, namely R1, at high frequencies but a bad loss tangent (C2+R2) at low frequencies.

Electrolytics are complex this way.

John

Thanks John, that was illuminating.

Hmm... all these network analyzers around... I probably ought to sweep an electrolytic one of these days...

"Hammy"

The low frequency (ie 100Hz) ESR is likely to be 3 or 4 times higher.

..... Phil

Thanks everyone for your help.

You would figure manufacturers would standardise their data sheets. When you're looking for a high ripple current and high temp capacitor they should just state the esr. ESR is a figure of merit. When I have to wade through 5 pages of possible capacitors I really don't feel like having to break out my calculator or decipher some graph, that's different in every manufacturer's data sheet.

Who ever does MultiComp and Muratas data sheets is a lazy SOB. Totally useless. No wonder their stuff is so cheap.

Anyways I found a smaller and cheaper one with an actual complete data sheet. I needed 6Arms current handling for 15Vdc output for a 100kHz fly back.

Three of these will do nicely plus an LC filter.

"Hammy"

D*****AD !!

YOU LYING TURD.

.... Phil

Why in all the SMPS application notes and books do they use the esr at

I knew the impeadance varied with frequency but I thought esr just varied over temp and manufacturing tolerances.

Bored Phill. Why dont you go out to the barn and visit the wife,or is your inbred father busy milking her.

I already have a job why should i do someone elses for them. If other manufacturers can state impeadance ,esr and ripple current in a nice neat colum that makes it QUICK and simple for value and capabilty comparsion why cant they?

Thats why I asked the question you bipolar kangaroo molester.

Touché! :)

Perhaps because the zero frequency is usually in the high hundreds-of-Hz to low-kHz range, so when data sheet ESR values are typically only available at, say, 120Hz and then 100kHz, the value at 120Hz is going to be a lot closer to reality than the one at 100kHz.

Additionally, perhaps, since it provides a more conservative design -- the calculated zero will be at a bit lower frequency than what the real circuit does, so if you've designed it to knock the gain back to

True ESR shows better at lower freqs. when you start to raise the freq of operation you then start to deal with induction that is commonly found in electrolytic and other types of caps the employ circular wrap constructions.

P.S. I know philis will have some commentary here, so hold on folks!

Thanks for the explanation.

Its just type two comp and only 100 kHz. I test mine with a load step. I can't afford a VNA:)

That's more than a lot of people do, so you're already ahead of the game. :-)

Be sure to try Joerg's trick of fooling around with quickly cycling the power as well, to make sure nothing goes "poof" at power-up.

---Joel

Jamie =

Maynard A. Philbrook = a LYING PILE OF S*IT

He is radio ham " KA1LPA " so par for the course.

Maynard is a genetic freak - he is part donkey.

He has the brain of one.

Heee, hawww........

...... Phil

Hammy are you listening? These guys just told you that ESR is not a single number! George H.

AVX do some good application notes on capacitors. It does not look like they have written one on ESR specifically, but the term is outlined in many of their other application notes.

Take a look at this:

... and finally...

if you want low ESR there are capacitors that are much better than the aluminium electrolytics you have chosen. this is probably why the ESR is not graphed in the datasheet