# Capacitance Decrease w/ Applied DC

• ColliLJ
In summary, the person is curious about why their 100uF 6.3V X5R dielectric ceramic capacitor decreases to approximately 60uF when a 5V DC bias is applied. They mention that the capacitance increases to 80uF when the DC bias is removed and explain that capacitance is normally constant under the working voltage for the component. The person then points out that some dielectrics can decrease in permittivity due to factors such as applied voltage or temperature and is seeking an explanation for this phenomenon.
ColliLJ
I would like to understand why my 100uF 6.3V X5R dielectric ceramic capacitor decreases to ~60uF under a 5V applied DC bias. Can anyone explain the physical phenomenon?

So, you applied 5V to 100uF cap and when you measured its capacitance by some equipment after removing supply it was 60uF. Am I right? Did you measured the capacitance at other voltages too?

Remember that capacitance is a constant and can't be changed normally if the capacitor is being used under the working voltage mentioned for that component.

The decrease in capacitance is while the 5V DC is applied. I can measure the capacitance at 60uF with an applied DC voltage. When I remove the 5V supply (DC Bias = 0V), the measured capacitance goes up to 80uF, which is just barely above the lower limit for the 100uF cap (+/-20%).

The capacitance is not constant! It's a well known phenomenon that some dielectrics decrease in permitivity as a function of an applied DC voltage, or an increase/decrease in temperature, etc. I just wanted to understand the phenomenon.

## 1. What is capacitance decrease with applied DC?

Capacitance decrease with applied DC refers to the phenomenon in which the capacitance of a capacitor decreases when a direct current (DC) voltage is applied to it. This is due to the accumulation of charge on the capacitor plates, which creates an electric field that opposes the applied voltage and reduces the effective capacitance.

## 2. Why does capacitance decrease with applied DC?

Capacitance decreases with applied DC because as charge accumulates on the capacitor plates, an electric field is created that opposes the applied voltage. This opposing electric field reduces the effective capacitance of the capacitor, as it makes it more difficult for the capacitor to store additional charge.

## 3. How does capacitance decrease affect circuit performance?

The decrease in capacitance can affect circuit performance in a few ways. One of the main effects is a decrease in the overall capacitance of the circuit, which can alter the circuit's ability to store and release electrical energy. This can also lead to changes in the circuit's frequency response and time constant.

## 4. Can capacitance decrease with applied DC be reversed?

Yes, capacitance decrease with applied DC can be reversed by removing the applied voltage. This allows the accumulated charge on the capacitor plates to dissipate and the electric field to disappear, resulting in the original capacitance being restored.

## 5. How is capacitance decrease with applied DC measured?

Capacitance decrease with applied DC can be measured using a capacitance meter. This device applies a known voltage to the capacitor and measures the resulting capacitance. By comparing the measured capacitance to the original value, the decrease in capacitance can be determined.

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