Typical ESR values

"Dishum"

In each case, the figure is for high frequency ESR or impedance at 100kHz.

ESR rises at low frequencies ( under 500Hz ) and falls with increasing temperature.

Also, when an electro goes bad (ie dries out ) - ESR rises first followed much later by a reduction in actual uF.

... Phil

That seems high for the tantalum. I seem to recall numbers like a couple tenths of an ohm. I'll try a couple. I don't have an ESR meter, but I can just apply a square wave from a 50 ohm generator and scope the voltage.

Hmmm, both of the 1u caps have about the same ESR.

John

I tried a standard leaded gumdrop tantalum, 1 uF at 35 volts, and got about 0.75 ohms.

Tantalum ESR tends to be in sort of a sweet spot for taming voltage regulators, both switchers and linear.

John

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I haven't used these spice models, but maybe something can be gleaned from them:

A brief Kemet paper:

Until they have exploded, that is :-)

Tantalums can be very reliable, much better than aluminums. You just have to handle them properly.

John

ftp://jjlarkin.lmi.net/Tant_ESR_Rig.JPG

ftp://jjlarkin.lmi.net/Tant_ESR_Scope.JPG

John

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Yes, suffice it to say, even though (dry slug) tantalums tend to have ESR comparable to (higher grade) electrolytics, they are far, far simpler: while lytics suffer from complicated ESL effects, tantalums are essentially the inductance of the body length and that's it. The equivalent circuit of C, ESR and ESL is very representative, and this makes ripple voltage much more manageble.

And of course, polymers are just about ideal, yadda yadda.

Tim

"Tim Williams is so full of s*it "

... Phil

Yup. On the gumdrops the leads are the most inductive part.

Yupyup.

John

If you keep dV/dT down, they are very reliable.

John

That sounds very reasonable. But there seems to be another quicker form of "goes bad" that happens with annoying regularity on PC motherboards - usually to the low voltage ram PSU capacitors but sometimes elsewhere.

I have just had an annoying incident with my own main PC motherboard where the ram PSU capacitors ATWB 1800uF 6.3v (nominally ultra low ESR) had started to bulge and over the past month a rock solid machine turned into something that required a several goes just to get past the POST. The situation seemed to be worst from a cold start after a weekend off and once warmed up the machine would become "reliable" after a fashion.

I thought all the bother with dodgy electrolytes outgassing had been fixed a long time ago, but I seem to have a similar fault on a modern board :(

I finally attacked the motherboard with a soldering iron today and was quite disappointed to find that at the low power and frequency my basic tester uses they measured as OK at 1820 and 1940uF and

"Martin Brown"

Thanks for this, but I can't measure series resistance down that low. It's just a quick and dirty tester.

That is certainly true. It seems to behave with the new capacitors in.

The bulging was the give away. The ones that bulged all had brown sleeves, an "X" on the end cap and were ATWB by maker Toshin Kogyo.

Datasheet tends to suggest that about 15mR is normal at 100kHz. (reading between the lines at 1800uF which isn't listed here)

The Rubicon 10v ZLJ part from its datasheet was good for 2.5A ripple and about 30mR @ 100kHz which is in the right ballpark.

Basically I couldn't measure the differences between them on the bench with a simple quick tester (and at low current).

Regards, Martin Brown

You don't always get to handle them before they explode John.... I had one double cap blow while I removed the lid of the computer.

--- Posted via news://freenews.netfront.net/ - Complaints to snipped-for-privacy@netfront.net

"The image ?ftp://jjlarkin.lmi.net/Tant_ESR_Rig.JPG? cannot be displayed because it contains errors."

I thought you were getting a real web site? Can't you use flikr in the mean time?

A technician had literally all tantalums explode when powering up a board. Luckily he wore eye protection. The company bought him a new shirt :-)

It's fine, never had a problem with any of Johns FTP images.

Must be you!

Tim -

Try: copy the link and paste into browser address bar.