The Causes of Electrolytic Capacitor Degradation
Most electrolytic capacitor degradation leads to a common failure mode: the vaporization or leakage of electrolyte.
To prevent electrolytic capacitor degradation in critical circuits, planned maintenance, replacement, or swapping of electrolytic capacitors should be scheduled at regular intervals.
The useful life of a capacitor is given in the electrolytic capacitor datasheet under nominal voltage, nominal current, upper category temperature with specified limits set on capacitance variation, tan ẟ, and leakage current.
Electrolyte leakage is one of the main failure modes in electrolytic capacitors
During a period from 1999 to 2007, there was a “capacitor plague” that resulted in a higher rate of premature electrolytic capacitor degradation. The cause of this particular issue was incorrect electrolyte formula, but there are several other failure modes possible in electrolytic capacitors. Capacitor failure modes introduce issues in a PCB and can be detrimental to the entire circuit.
Because of the past challenges with electrolytic capacitor degradation, buyers are now extra cautious about the durability and lifespan of electrolytic capacitors, as they are necessary elements in many circuit designs. It is important that designers understand what causes electrolytic capacitor degradation.
Electrolytic Capacitor Degradation Due to Electrolyte Leakage
When an electrolytic capacitor fails, it can be because of a short circuit, circuit damage, or even an explosion. Most electrolytic capacitor degradation results from a common failure mode: the vaporization or leakage of electrolyte.
The high operating temperature is a catalyst to electrolytic leakage or vaporization and leads to a decrease in capacitance and an increase in equivalent series resistance (ESR). As ESR increases, there is intensified self-heating in the electrolytic capacitor, and the same gets accelerated with the application of ripple currents. Localized hotspots formed by excessive heating speed up aging and wear-out failure modes, ultimately leading to electrolytic capacitor degradation. In the worst cases, self-heating develops gases inside the electrolytic capacitor, which subsequently explode the electrolytic capacitor through the vent.
Other Causes of Electrolytic Capacitor Failure
Electrolyte leakage is not the only failure mode in electrolytic capacitors. Other failure modes of electrolytic capacitors are listed in the table below.
To prevent electrolytic capacitor degradation driven by the aforementioned failure modes in critical circuits, planned maintenance, replacement, or swapping of electrolytic capacitors should be scheduled at regular intervals during their useful lifespan. Usually, the useful life of an electrolytic capacitor is listed in its datasheet. However, the applied voltage, ambient temperature, local heating, reverse voltage, applied ripple currents, and frequency of operation have a significant influence on the useful lifespan of electrolytic capacitors. Understanding the electrolytic capacitor lifespan under operating conditions is helpful for circuit design as well as circuit maintenance.
The Useful Life of Electrolytic Capacitors
Due to aging and in-circuit service under different mechanical and electrical conditions, an electrolytic capacitor may fail. Electrolytic capacitor failure is always preceded by a decrease in capacitance, an increase in ESR, and an increase in tan ẟ. As the internal damage in an electrolytic capacitor matures, the probability of failure increases. It is important to replace or swap an electrolytic capacitor before it fails.
The useful life of a capacitor is given in the electrolytic capacitor datasheet under nominal voltage, nominal current, upper category temperatures with specified limits set on capacitance variation, tan ẟ, and leakage current. The useful life of an electrolytic capacitor is application-specific and can be calculated using the equation:
LX is the resulting lifetime, L0 is the lifetime specified in the datasheet under nominal conditions, KT is the temperature factor, KR is the ripple current factor, and KV is the voltage factor.
The temperature factor is given by:
T0 and Ta is the upper category temperature and the ambient temperature of the application, respectively.
The ripple current factor is given by:
, IA is the application ripple current, I0 is the nominal ripple current at upper category temperature, T0 is the core temperature rise of the electrolytic capacitor, and Ki is the empirical safety factor.
The voltage factor KV is given by:
Ua is the actual operating voltage, Ur is the rated voltage, and n is the exponent.
Electrolytic capacitor degradation is challenging, as it limits the reliability of critical circuits. Cadence’s PCB design and analysis software can help designers identify reliable electrolytic capacitors for circuit design.
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