How Temperature and Electrical Factors Influence Electrolytic Capacitor Lifespan

Key Takeaways

• The most common reason for reduced electrolytic capacitor lifespan is the evaporation or leakage of the liquid electrolyte. 

• The electrolytic capacitor lifespan or service life is defined in the datasheet under nominal voltage, nominal current, upper category temperature with specified limits set on capacitance variation, dissipation factor (tan ẟ), and leakage current. 

• The electrolytic capacitor lifespan should be several times greater than the load life under the actual operating conditions.

Electrolytic capacitors are some of the oldest capacitor technology in use today

Electronic circuits rely on DC-DC converters and AC-DC converters for their operation. Converters are the source of power supply in electronic circuits. DC-DC converter power supplies step up or step down the battery voltage to the required amplitude. AC-DC converter power supplies produce the desired DC voltage for circuit operation from the supply mains.

There is at least one electrolytic capacitor used in the power supplies for electronics circuits, and the reliability and service life of the power supplies are dependent on the electrolyte capacitor’s lifespan. Unfortunately, electrolytic capacitors are vulnerable to degradation, failures, and wear out, mainly due to electrolyte leakage. It is important to have a clear understanding of the electrolytic capacitor lifespan before using them in power supplies.   

Electrolytic Capacitor Lifespan 

Electrolytic capacitors are some of the oldest capacitors in use today. They are also the most critical capacitor type due to their limited lifespan. The lifespan of electrolytic capacitors is very brief. They are most often subject to failures, which are categorized as early failures, random failures, or wear-out failures. The mean time between failures (MTBF) of electrolytic capacitors is low compared to the calculated MTBF of the electronic circuits where they are used. There is an expiry date associated with any electrolytic capacitor in use. The expiry date or end of life can be pushed by operating the electrolytic capacitor under ideal environmental, mechanical, and electrical conditions.

The most common reason for reduced electrolytic capacitor lifespan is the evaporation or leakage of the liquid electrolyte. Other failure modes of electrolytic capacitors that are capable of depreciating the service hours of the capacitor are open circuits, short circuits, and open vents. 

Environmental and electrical factors also play a role in the service life of electrolytic capacitors. The environmental factors listed below influence the useful lifetime of these capacitors:

• Humidity
• Temperature
• Atmospheric pressure
• Mechanical vibrations 

And, the electrical parameters below also play a vital role in the premature failure of electrolytic capacitors:

• Charge-discharge duty cycle
• Applied voltage
• Ripple current 

Factors Influencing the Electrolytic Capacitor Lifespan

The electrolytic capacitor lifespan or service life is defined in the datasheet under nominal voltage, nominal current, upper category temperature with specified limits set on capacitance variation, dissipation factor (tan ẟ), and leakage current. The useful life of an electrolytic capacitor is application-specific and can be calculated using the equation:

L_X is the resulting lifetime, L₀ is the lifetime specified in the datasheet under nominal conditions, K_T is the temperature factor, K_R is the ripple current factor, and K_V is the voltage factor. The temperature, ripple current, and apple voltage can accelerate aging and diminish the time gap between consecutive failures in electrolytic capacitors. 

Temperature

The temperature aggravates the aging of electrolytic capacitors due to the increase in the chemical reaction rate. A rise in temperature significantly increases the capacitance drop, tan ẟ, and ESR and leads to the gradual evaporation of the electrolyte through the seal. The self-heating and temperature rise are critical when considering the electrolytic capacitor lifespan in power applications. The term K_T in the equation below can be expanded, as given in the second equation listed, and brings corresponding  depreciation in the electrolytic capacitor lifespan.

T₀ and T_a are the upper category temperature and ambient temperature of the application, respectively.

Voltage 

The life expectancy of an electrolytic capacitor is influenced by the applied voltage as well as the reverse voltage across it. Under nominal voltage conditions or below that, the lifespan of an electrolytic capacitor is less affected by operating voltage. Applying an excessive voltage across the electrolytic capacitor increases leakage current. The leakage current is responsible for internal gas generation and self-heating in an electrolytic capacitor, which ultimately damages the capacitor’s internal structure, resulting in the possibility that the device is blown off. The reverse voltage above a few volts builds up internal heating and pressure. If an electrolytic capacitor is subjected to high reverse voltage, it may fail from the opening of the safety vent. The decrease in the electrolytic capacitor lifespan due to operating voltage is given by the voltage factor K_V.

 U_a is the actual operating voltage, U_r is the rated voltage, and n is the exponent.

Ripple Current 

The ripple current flow through an electrolytic capacitor produces more internal heat. The self-heating and temperature rise significantly deteriorates the useful service period of the electrolytic capacitor. The reduction of the electrolytic capacitor lifespan under nominal conditions due to current ripple is given by the ripple factor K_R .

, I_a 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 K_i is the empirical safety factor.

Charge-Discharge Duty Cycle 

Discharge currents are catastrophic to electrolytic capacitor lifespans. The discharge current increases the internal heating and pressure, which reflects as the capacitance value drop during initial stages. With time, the charge-discharge duty cycle may lead to the destruction of the electrolytic capacitor by opening the safety vent to release gases.

To ensure the long life and reliability of electronics, electrolytic capacitor lifespan should be carefully selected so that it is several times greater than the load life under the actual operating conditions. Cadence’s suite of design and analysis tools offers reliability analysis to estimate the reduced lifetime of a device due to environmental and electrical parameters.

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