I found interesting article about capacitance of ceramic capacitors may depend on voltage applied.
It seems to be that in some designs you can face a problem when ceramic capacitor capacitance may strongly depend on voltage. Few tests were done with various capacitors using following circuit:
In the circuit CX â€“ tested capacitor; C0 â€“ known capacitor. Voltage vas regulated from 0 to 50V using potentiometer R1. 50V is taken as nominal voltage of ceramic capacitor. Because Two capacitors are connected in series the total capacitance is C=CXÂ·C0/(CX+C0) then we find capacitance of tested capacitor CX=CÂ·C0/(C0-C); C0 â€“ is about 10 % of CX value.
There were several capacitors tested and stunning results were found. – Some of capacitors lost capacitance from 10 to 15 times due to increase of voltage up to 50V. Even when 10% of voltage were applied the capacitance was only about 35 â€“ 40% of nominal value.
One and only explanation may be that low quality dielectric material is used in (no-name) ceramic capacitors. Of course not all capacitors gave following results. But be ready for this when using unknown producer ceramic capacitors.