Tantalum Capacitor

Depends on the application.
A good quality electrolytic may do the job, but it depends what 'the job' is.
Del

thanks for your help

It depends greatly on the application the capacitor is being used for and the frequency it is being used to pass/filter/block/etc.

Can you please elaborate and explain your circuit and application?

this capacitor is used on the input and another one on the the output of TL317 regulator

Are you changing the design to try to make it cheaper, or, are you repairing a faulty unit?

If you're changing the design: then be aware that electrolytics dry out over a period of time, so you have to make sure that the new part will last for the projected lifetime of the product.

If you're repairing a (or several) faulty unit(s) then: I would wonder why the tantalum failed. Tantalums need to be overrated in all designs but especially where they are subject to switching spikes: are there any other switching supplies of the same rail?

Now I see he is using this capacitor to block oscillation in the regulator circuit. These simple 3 and 4 terminal regulators are susceptable to this oscillation, which can take place at high frequencies. They call this 'parasitic oscillation', and it can occurs in all

manner of circuits. It is just like mike feedback. Mike feedback is often a squeal, but can also be supersonic in high quality circuits.

here are some links.

http://www.google.ca/#hl=en&source=hp&q=%22parasitic+oscillation%22+%2Bregulator&btnG=Google+Search&aq=f&aqi=&aql=&oq=%22parasitic+oscillation%22+%2Bregulator&gs_rfai=&fp=2a80292b88be7c76

In that case it is not critical that these capacitors be of Tantalum type. Electrolytic or other type capacitors are fine for this type of linear regulator.

A quick check of the corresponding data sheet confirms this, page 4 "Application Information" (these bypass capacitors are optional but are recommended).

http://www.datasheetcatalog.org/datasheet/texasinstruments/tl317.pdf

Sometimes these tantalum capacitors ( or condensers.) are chosen for specific reasons.

I believe tantalum type are best for timing circuits as they are very stable in performance and can survive better in hard environments.

If it was a repair for me I would use the same type if it was tantalum.

Tchau.

Ummmm? Tantalum is a chemical. So is oxygen, silicon dioxide,,, damn, in fact it turns out that most things we can see, touch, eat, build with,, whatever,, they are all CHEMICALS,,,,,

Now, can you be more specific?

Cheers

Martin

tantalum is chosen for its permanence as well as its high capacity per unit volume. Aluminium caps are 2-5 times larger for the same capacitance and voltage.

All other foil and film capacitors are very much larger than these electrolytic capacitors.

Tantalum sponge with an insulating solid electrolyte has a huge surface area.

refs here

http://www.google.ca/#hl=en&source=hp&q=wiki+%2B%22tantalum+capacitor%22&btnG=Google+Search&aq=f&aqi=&aql=&oq=wiki+%2B%22tantalum+capacitor%22&gs_rfai=&fp=2a80292b88be7c76

All true, but without knowing the application, it's impossible to say. What if it's a high voltage power supply? What if it's interstage coupling and requires non polarized capacitors?

His application is a low voltage electrolytic. Tantalum capacitors can not be made in high voltage or as non electrolytic types. Electrolytics are also low frequency and are not suited to be bypass caps for digital noise. Electrolytics are suited to low frequency power fluctuations.

That is why you see mother boards with both tantalums and ceramic caps between the same 2 rails

The so called NP capacitors made with two electrolytics - to -, are not true NP capacitors. NP = non polarized.

"His application is a low voltage electrolytic" Sorry I missed that post. Tantalums are usable to much higher frequencies than electrolytics, but are still far from a true high freq. cap. The biggest problem with tantalums is their relatively high ESR,, but since he already has a tantalum in there, why go with something else?

tantalums are costly and hard to find in some values. If he meets the voltage and capacitance required, he can tolerate a larger capacitor in most cases.

I've been an electronic technologist since 1979,, without knowing the specific application, I wouldn't give advice either way.

since 99% of tantalums are used in power supply rails on motherboards and assorted computer boards, I judge this fellow has had some stinkers (when tantalums pop, they stink) and he wants to replace them. There were a rash of bad tantalums a while back. He finds the exact part hard to get. He may not be in a major supply nexus, like the UK, USA, Japan, so he wants to fix it with aluminiums. He does not realize that with power supply filtering, as long as you exceed the voltage rating, you can cobble together anything with a rats nest of wire tp do the task. It may not look good, but in extermis, it will work.

Well, as a sailor, I have to quote part of Rule 7 of the COLREGs,, "Assumptions shall not be made on the basis of scanty information"

well, lets see if he supplies more data

Usually tantalum capacitors are used also for their high frequency performance, for decoupling purposes, much better than electrolytics,

if it is for a repair, better to use same type, but if you do not have access to a tatntalum capacitor, I suggest to use a ceramic capacitor 100nF in parallel with the chemical one you will use

B/R

You'll probably get away with a good quality electrolytic on a regulator input, if you put a 0.01uF or 0.1uF ceramic across it for good measure. This is just guess work of course as it depends on what the regulator is driving, clock frequency, load etc.
if you go with a slightly higher value too you'll probably be ok.
The real Q is why did they design in an expensive component if a cheaper one would have done the job?
I get irritated when press me to change things on designs and then wondering why they cease to function.
Del

Uses

The low leakage and high capacity of tantalum capacitors favors their use in sample and hold circuits to achieve long hold duration, and some long duration timing circuits where precise timing is not critical. They are also often used for power supply rail decoupling in parallel with film or ceramic capacitors with low ESR and reactance at high frequency. Tantalum capacitors can replace aluminum electrolytic capacitors in situations where the external environment or dense component packing results in a sustained hot internal environment and where high reliability is important. Equipment such as medical electronics and space equipment that require high quality and reliability make use of tantalum capacitors.

Low-voltage tantalum capacitors are commonly used in large numbers for power supply filtering on computer motherboards and in peripherals due to their small size and long-term reliability.

Ref to for detailed info:

Tantalum_capacitor

Tip:

In 3 pin regulators [fixed voltge or variable voltage] mica capacitors are used due to low ESR not tantalum capacitor to filter noise.

Also refer to

Tantalum Capacitors given at the end of posts.

I swapped out a tant for a chem. I have not lost any sleep over it and my pacemaker hasn't skipped a beat yet. All aside, I really enjoyed the depth of y'all's knowledge, learned alot and now know some of the pitfalls of caps and their applications. Thanks!

The bypass capacitor for your input into the Tl317 can be any standard electrolytic and the same goes for your output of the Tl317 which would improve your transient response. So yes, you can replace your Tantalum, but pay attention to the capacitance value during conversion from Tantulum to standard electrolytic caps.

what do you mean by pay attention to the capacitance value when replacing tanl. with chem?

Just make sure it has a similar capacitance value (in uF). An electrolytic capacitor has a much greater capacitance than a similar physically-sized Tantalum capacitor.

Huh?

Here are two fairly typical 100µF 25V caps from Digikey

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=399-5175-2-ND

Tantalum 7343-43 7.3 mm long by 4.3 mm wide by 4.3 mm (max) high

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PCE3298TR-ND

Aluminium electrolytic 8mm diameter 6.2 mm high

NO! Replace with as designed. All else has been addressed by previous. One thing that otherwise would have to be verified is if the regulator would go into oscillation under any load condition or between.