Ceramic Capacitor Voltage Derating

Formula

Description

Class II and Class III ceramic capacitors (X7R, X5R, Y5V, Z5U) lose significant capacitance when a DC bias voltage is applied. A 10 µF X5R capacitor rated at 10 V may lose 50-80% of its capacitance when biased at 8 V. The derating factor represents the fraction of rated capacitance available at the operating DC bias. This effect is a fundamental material property of high-permittivity ceramics (barium titanate) and cannot be designed out. Class I ceramics (C0G/NP0) do not exhibit this effect but are limited to small capacitance values.

Variables

• C_eff — Effective capacitance at operating voltage (F)
• C_rated — Rated (zero-bias) capacitance (F)
• factor — Derating factor (0 to 1)

Practical Notes

Always check the manufacturer DC bias curves when selecting MLCC capacitors. A common rule of thumb is to derate by 50% for X5R/X7R at half the rated voltage, but actual derating varies significantly between manufacturers and packages. Larger case sizes generally have better voltage derating characteristics. Consider using multiple smaller-value capacitors in parallel to mitigate derating effects.