Tantalum Cpacitance [hlp]

[elec350]

tantalum capacitor infant

hello
Pls explain about Tanalum Capacitance. What's its application? Must we use it for power supply circuit of RF circuits? Why and where?

 

[tshah]

Yes, tantalum capacitance are used in power supply line filtering because they have very high effective series resistance (ESR) value which is critical for stability. Usually tantalum capacitors are placed after the output of regulated supply and before the input in to the regulator to limit the high frequency and low frequency noise. 10 uf capacitor can drain out all the low frequency noise because it provides low impedance path to low frequency signals and 0.1 uf can be good enough to drain out high frequency noise signals. You can put both capacitors at the input and output side of regulator.

Thanks

 

[House_Cat]

Actually, the ESR (effective series resistance) of tantalum capacitors is about 10 times LOWER than other types of capacitors with the same values such as aluminum can electrolytics.

They have an almost unlimited lifetime, and they are many times smaller than other high value capacitors with the same voltage rating.

They are used for power supply filtering because they are small, efficient, and long lived.

 

[ender84567]

Agree with house cat about ESR however lifetime I would disagree, with tantalums you need to derate by at least 50% better would be 75% and you are looking at an initial fallout of 1-2 % due to forming unless you are using screened parts. Tantalums are generally smaller than traditional electrolytic and are used when you need a lot of bulk capacitance in a small package, or can be used when you need a low esr capacitive input. (WRT other capcitors, ceramics are lower ESR but in higher uF values become bulky and are susceptible to cracking under vibration.)

 

[House_Cat]

ender84567 - Tantalum capacitors have an unlimited shelf life because they are 100% dry dielectric. They are self healing - if an oxide layer failure occurs, they tend to form a new manganese dioxide film at the point of failure with a higher film resistance than the original film.

I suggest if you have to derate by 50% and experience 1-2% infant mortality, you need to change suppliers. If you buy the cheapest junk on the market, you get what you pay for. Stick with reputable brands - Vishay, Kemet, NEC, AVX, etc.

 

[tshah]

Hi,
I would like to accept one of my mistake which I made in the statement above that "Tantalum Caps have higher ESR" it is not true. Tantalum caps have lower ESR value and the reason to choose them is to reduce ripple voltage on the power supply line. Because the ripple voltage is = I * ESR. So, if you have higher ESR it will contribute to ripple voltage.

Another thing I didn't understand from the conversation between HOUSE_CAT and ender84567 is that what do you derate? the value of capacitor or ESR? like for example if I need 2 ohms ESR, I would choose a part which has 1 ohm ESR? I don't understand that conversation. Please clarify me.

Thanks

 

[House_Cat]

Hi Tshah,

Derate means to use the capacitor at a lower voltage than the rated working voltage. In other words, if you have a capacitor rated 15WVDC, and you derate 50%, you would only use it in circuits with up to 7.5VDC.

There are at least three reasons that derating might be necessary -
1. The capacitors are poorly made, and can't really operate at their rated voltage. 2. The circuit is poorly designed and the voltage buildup is too fast for the capacitor causing a high peak charging current (can physically blow up the capacitor).
3. The capacitor is going to be operated close to, or above, its rated temperature limits (again poor design).