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Electrolytic Capacitors Information Page
Function of Electrolytic Capacitors.
Capacitors act as an electrical accumulator, taking in excess power to help maintain a constant voltage
or power level. Analogous to a shock absorber in a car, the capacitor acts to slow any changes in the
input power, while allowing a metered amount of energy to exit. In the automobile, bumps in the road cause
the changes in input power, and the result of slowing these changes is a smooth ride. In the electrical
circuit, the capacitor takes variations in the input and creates a regulated output. The difference between
the input and output, ripple current energy converts to heat within the capacitor.
In a typical switching power supply electronic applications, the electrolytic capacitor takes delivered AC
power and converts it to a constant voltage output. Since mechanical components are becoming increasingly
sensitive to voltage transients, the demand on electrolytic capacitors and the heat generated by this demand
continue to increase.
In many high power applications, such as CPU power supply and switching power supplies on the motherboards,
multiple capacitors work together to achieve regulated input power. In some cases, as many as 10 or 30 large
capacitors are required to achieve system isolation from power or voltage loads. Each of these parts shares
the input ripple voltage load and will equally share the heat accumulation.
Why do capacitors fail?
Electrolytic capacitors use a semi-liquid electrolyte inside the case to make electrical contact
with the foil windings. This electrical interface is inherent in the capacitor's ability to carry
current and function as an energy storage unit for the electrical power input. When the interface
between the electrolyte and the metallic foil windings begins to degrade, the electrical connection
begins to fail. Heat build up is the primary cause of this degradation, which, depending on severity,
can cause either short-term catastrophic failure, or long term functional degradation. The life expectancy
of an electrolytic capacitor relates directly to its internal temperature. Every 10° C increase in internal
temperature halves the component lifetime.
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