Monday, April 15, 2024

Ceramic capacitors and DC biasing

I am considering replacing many of the high value capacitors in my circuits, which are usually electrolytic caps, with ceramics.

There is however an issue -  ceramic caps have a strange property: if they are DC biased, e.g. normally have a certain voltage across them, the effective capacitance changes:

https://community.infineon.com/t5/Knowledge-Base-Articles/DC-Bias-characteristic-of-Multilayer-Ceramic-Capacitor-MLCC/ta-p/250035

ReddyAn_0-1707370124509.png

The capacitance change is relative to the capacitor size, so 1206 caps do not change as much as 0603 for example. The voltage rating however, has little effect.

As an example, if one side of the cap is connected to ground, and the other has a signal that swings around 4V, the effective capacitance will be just 30% of the rated value if we're using an 0603 cap. Using a 1206 instead gives around 70%.

C0G caps are not as affected by this as X7R, X5R, but in return they are bigger and not readily available in as high capacitances.

https://www.kyocera-avx.com/docs/techinfo/CeramicCapacitors/mlcc-dc-bias-characteristics.pdf

 

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