Does the ripple current specification in capacitors matter?
Too much ripple current leads to heat generated in the capacitor. When the heat generated by the ripple current exceeds the maximum allowable core temperature of the cap, damage is done. Even if heat doesn’t make the capacitor immediately fail, heat is directly related to the failure rate over time.
Ripple current capacity is affected by the physical size of the capacitor and its concurrent ability to dissipate heat. A smaller capacitor can be saturated with heat and fail earlier than a larger capacitor with more mass and more surface area. The thermal interaction with its environment and internal thermal resistance also determine the capacitors ability to handle ripple current and heat.
The Equivalent Series Resistance (ESR) of the capacitor dictates how much current is converted into heat. The most common way of enhancing the ripple current capability of electrolytic capacitors is by minimizing the ESR. Low ESR means less current is converted to heat, and generally a higher ripple current specification. The ESR of capacitors also varies dependent on frequency. The ESR can vary greatly over a range of frequencies, the operating frequency in the application must be ensured to stay in the specified range for the ESR to remain in its useful values and keep ESR down.
ESR specification in capacitors is not standardized, so it is important to verify that the given ESR from the manufacturers test conditions matches your application conditions. Another way to deal with ESR and temperature specification is to de-rate the operating voltage when using them at higher temperatures.
In most capacitors ripple current and equivalent series resistance determines the temperature rise. Choosing capacitors with low ESR helps to minimize power dissipation and enhance the capacity of the circuit to withstand high ripple currents. The life of your circuit is largely dependent on your capacitors, and the life of your capacitors is greatly determined by internal temperature, making it very important to minimize the heat generated by ripple current that kills the capacitors.
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