Using SPICE to Measure Effective Capacitor Ripple Current (Download)
Robustness in a power-supply design is based on predictable, long-term service life. In conventional switch-mode power supplies (SMPS), this is most often dictated by the characteristics of aluminum electrolytic capacitors. However, these components, sometimes called Al-Ecaps, degrade over time. As a result, accurate estimation of capacitor lifetime requires precise calculation of the ripple current, which is the primary cause of that degradation.
One approach is to use oscilloscope-captured data from a power supply and Fast Fourier transform (FFT) analysis in LTspice to evaluate all factors that can cause current ripple. With this approach, verifying the effective ripple current and resulting internal temperature rise of the capacitor can be achieved without resorting to expensive equipment or relying on oversimplified approximations. This article provides power-supply designers with a step-by-step guide.
