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X5R capacitors derate to about roughly 85% when DC voltage is applied, from what I have been told.

Does this have an effect on high pass filters, even though HF filters off DC (0Hz)? If I wanted to test voltage derating on capacitors and its effect on an AC signal, how would I do so?

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I tried with different frequency and tried adding a Voltage offset, and these were the results i got. When I simulated it didn't show any change. When i tried to run a test on a small HF circuit with a 100nF X5R capacitor and a 1k, the amplitude of my output reduced. At higher frequencies the changes in amplitude were wayy smaller compared the frequencies at and under the cutoff frequency((1446Hz).

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  • \$\begingroup\$ What is your peak voltage for any DC component and the HF ripple? \$\endgroup\$
    – winny
    Commented Feb 13, 2019 at 14:07
  • \$\begingroup\$ It's much cheaper to buy the cap that you need, rather than use a cap that's not and test it. \$\endgroup\$
    – Scott Seidman
    Commented Feb 13, 2019 at 14:10
  • \$\begingroup\$ The X5R capacitor i'm currently using is 100nF capacitor with a voltage rating on 10V parallel with a 1.1kohm resistance. So it's cutoff freq is about 1446 Hz. When testing the output of a 1460 Hz sinewave with a 9.6Vpp, the result of the scope gave a slighty sine with lower amplitude. \$\endgroup\$
    – Vinh Trung Thai
    Commented Feb 13, 2019 at 15:14
  • \$\begingroup\$ Scott Seidman. I wanted to see the characteristics of the X5R capacitor and it's effect on a sine wave \$\endgroup\$
    – Vinh Trung Thai
    Commented Feb 13, 2019 at 15:15
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    \$\begingroup\$ What is the TOLERANCE of your cap? If it's 20%, your capacitance can be anywhere between 80 and 120 nF. \$\endgroup\$
    – Scott Seidman
    Commented Feb 13, 2019 at 15:32

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"Derate" doesn't necessarily mean that the capacitance value changes -- it just means that some of the specs change. For example, if the voltage rating for a 0.1 microfarad cap is 40V, derating by 75% would mean that you should not use it past 30V.

So, if you planned to use your high pass filter constructed with the above capacitor at above 30V, and it's spending most of it's time at DC, or with a large DC offset, then yes, it is "affecting" the functionality of the circuit.

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    \$\begingroup\$ Multilayer cap derating have to refer to manufacturer datasheet. As the applied DC voltage reaching the rated voltage of the cap, the higher the capacitance loss. \$\endgroup\$
    – Jason Han
    Commented Feb 14, 2019 at 8:44

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