Electrolytic Capacitor

An electrolytic capacitor is a sort of capacitor that utilizes an electrolyte to obtain greater capacitance than the other type of capacitors. An electrolyte is a gel or fluid in which concentration of ions is very high. Electrolytic capacitor is a general term used for three different capacitor family members:

  • Aluminium electrolytic capacitors
  • Tantalum electrolytic capacitors
  • Niobium electrolytic capacitors

Electrolytic Capacitor

Almost all the electrolytic capacitors are polarized which means the voltage of anode must be always higher than the cathode. The ability of large capacitance makes them highly useful for sending low-frequency signals. They are extensively used for noise filtering or decoupling in power supplies. The advantage of large capacitance comes with few drawbacks as well. Drawbacks include leakage currents, equivalent series resistance and a limited lifetime. Electrolytes are made up of aluminum or tantalum and few other metals.

A special type of electrolytic capacitors with capacitances of hundreds and thousands of farads are known as supercapacitors. They are also known as double-layer electrolytic capacitors.

Characteristics:

Capacitance Drift:

The electrical characteristics highly depend on the type of electrolyte used and the anode. The capacitance of electrolytic capacitors have large tolerances 20% and drifts from nominal value as the time passes. This implies aluminum capacitor whose nominal capacitance is 47µF is expected to have a value between 37.6µF and 56.4µF.

Tantalum capacitors can also be made with higher tolerances, but their maximum operating voltage is very low. So they cannot be used as perfect replacement aluminum capacitors.

Capacitance, Standard Values and Tolerances:

The electrical characteristics highly depend on the type of electrolyte used and the anode. This affects the value of capacitance which again depends on temperature and frequency. The capacitors which contain nonsolid electrolytes display a wide sense over temperature and frequency ranges than capacitors with a solid electrolyte. The base unit of the capacitance of an electrolytic capacitor is microfarad. The capacitance value that is specified by the manufacturers in the data sheets is called nominal capacitance or rated capacitance. The value of capacitance measured at the frequency of 1 kHz will be less by 10 percent of 100/110 Hz and where the temperature is \(20^{\circ}C\).

The percentage of allowed deviation of measured capacitance from the rated value is called the capacity tolerance. These capacitors are handy in variety of tolerance series whose values are specified.

  • rated capacitance, tolerance ±20%, Series E3, letter code “M”
  • rated capacitance, tolerance ±20%, Series E6, letter code “M”
  • rated capacitance, tolerance ±10%, Series E12, letter code “K”

Applications:

  • Used to reduce voltage fluctuations in various filtering devices.
  • Used in output and input smoothing to filter when DC signal is weak with AC component.
  • They are extensively used for noise filtering or decoupling in power supplies.
  • They are used for coupling signals between amplifier stages and also to store energy in flash lamps.

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Practise This Question

The graph gives the magnitude B(t) of a uniform magnetic field that exists throughout a conducting loop, perpendicular to the plane of the loop. Rank the five regions of the graph according to the magnitude of the emf induced in the loop, greatest first