Expected lifetime and failure rates are based on the component’s rated voltage. The rated voltage is usually lower than the “breakdown voltage”, which depends on the capacitor’s dielectric-typed and rated voltage.
Typically for MLCCs up to 200 V, the breakdown voltage is 4x rated. While parts rated for 200 V up to 1,000 V the breakdown voltage may be up to 1.2X rated. Parts over 1,000 V may have a breakdown such as 1.15X rated. (Please see a capacitor’s datasheet for specified values.) These breakdown multipliers will decrease with increasing temperature.
The breakdown voltage does not change over frequency. However, the impedance of a capacitor is lower with higher frequencies. This change in impedance may see a rise in ripple current. The current increase creates a self-heating, dependent on the component’s ESR.
Calculating Power Loss
The power loss (PLoss) of the MLCC requires a reduction in voltage to keep the current below a limit the power limit of the capacitor.
Figure 1 – KEMET K-SIM Example
For power calculation use the RMS (root mean square) values.
The VRMS = Vr/ √2 is only valid for sinusoidal waveforms. For other waveform shapes, use the integral shown in Equation 2.