Polar Tantalum Capacitor

Electric circuits like power supply filters, which do not have batteries, use capacitors to store a charge and yield it when there is a fluctuation in the voltage and current output. The element tantalum is used to make tantalum capacitors since the element has more capacitance per volume than other materials like aluminum. They are called polar since they have separate positive and negative terminals. They are also used in circuits that require only AC current to be conducted while blocking DC.

How It Works:

These capacitors are made of two electrodes. The cathode electrode is made of sintered tantalum and deposited with a thin layer of oxide. The layer of oxide induces a very high capacitance per unit volume. The anode electrode is made of a chemically deposited semi-conductive layer of manganese dioxide and connected to an external wire lead. Paper separators are used. Capacitance is formed between the anode foil and the electrolyte.

Polar Tantalum Capacitor Design Consideration:

Capacitors are available with ratings of 1 MF to 1000 MF in voltage ratings from 2 V to 50 V. While they have temperature stability, volumetric efficiency and general compatibility, their main weakness is limited voltage and capacitance range and their tendency to explode when subjected to spikes or reverse biased. Key factors to be considered are:

Temperature range in which the capacitor functions is around –25deg to +55deg C.
Temperature at which the capacitor can be stored and retain its properties.
Rated capacitance: the nominal capacitance (e.g. 22 µF at 50 V).
Capacitance tolerance: maximum and minimum percentage allowed on the rated capacitance (e.g. 5%).
Capacitance measurement: comparison when measured in a measuring bridge in a lab for an equivalent circuit at 25 deg C with a 120 Hz supply.
Variation with temperature: should be less than 10% at –40 deg C.
Dissipation factor: ratio of the ESR (equivalent series resistance) to the capacitive resistance.
Impedance: ratio of voltage to current at a fixed frequency. 

Polar Tantalum Capacitor Types:

Classification is done as per ratings and construction. They are available as SMT (surface mount technology) or non-surface mount devices (leaded) and sold in molded and can style, axial and leaded can style. Based on their lamping, they are available as snap-in terminals and large can screw terminal styles. A typical rating would be 22 MF at 35 V.

Polar Tantalum Capacitor Applications:

Tantalum capacitors are used in stable spike-free areas that require high capacitance and where there is a constraint for weight and space. Typical uses are: power synchronous boost converters, load-transient response of LDOs, high-speed data converters. Other areas where they are used are operational amplifiers, off-line lithium-ion chargers, USB power distribution systems, basic analog passive devices, cable transceivers, etc.