Overview

It is known that the capacitance of ceramic capacitors, which are the mainstream of capacitors, changes depending on the conditions of use.

This time, we will explain the capacitance change using the data of the ceramic capacitor of Wurth Elektronik as an example.

Classification of ceramic capacitors

Ceramic capacitors are generally classified into two types: temperature compensation type and high dielectric constant type, and their features are as follows.

・Temperature-compensated capacitors do not have a large capacitance, but their capacitance changes little due to voltage, temperature, and other factors.
・Since high dielectric constant materials are used for high dielectric constant materials, a large capacitance can be obtained, but capacitance changes occur due to various factors.
When using a high dielectric constant system, it is necessary to select after understanding the capacitance change that occurs.

Figure 1 shows the classification of temperature characteristics for temperature compensation in the EIA standard.

Figure 1: Classification of temperature characteristics of ceramic capacitors for temperature compensation

From Wurth Elektronik ANP062​

From this, it can be seen that for the C0G characteristic, the temperature change is extremely small at ± 30ppm/ °C.

Figure 2 shows the classification of temperature characteristics for temperature compensation in the EIA standard.

Figure 2: Classification of temperature characteristics of high dielectric constant ceramic capacitors

From Wurth Elektronik ANP062​

From this it can be seen that for the X7R characteristic, the temperature change is within ± 15% over the operating temperature range of-55 to 125 °C.

DC bias characteristics

In high dielectric ceramic capacitors, it is necessary to consider the influence of DC bias characteristics. DC bias characteristics refer to the phenomenon in which the capacitance decreases when a DC voltage is applied, and it is important to note that the characteristics change not only with the applied voltage but also with temperature characteristics and size.

Figure 3 is a typical example of DC bias characteristics. It can be confirmed that the capacitance of the high dielectric constant system decreases due to the DC bias, and the DC bias characteristics differ depending on the temperature characteristics. Even X5R/X7R, which have good characteristics, will have a capacity less than half of the nominal value if used near the rated voltage.

Figure 3: Representative example of DC bias characteristics

From the website of Wurth Elektronik​

Also, the DC bias characteristics will vary depending on the size even if the product has the same nominal capacitance, withstand voltage, and temperature characteristics. Figure 4 shows the results of comparing three sizes of 10 μF /10V/X7R ceramic capacitors with Wurth Elektronik 's design tool REDEXPERT.

Figure 4: Effect of DC bias characteristic size

From this comparison, it can be seen that the capacitance difference between the 2012 size and the 3216 size is more than double when used with a DC bias of 6V. For this reason, it is necessary to check the DC bias characteristics of each component, not the characteristics shown in the typical characteristics example.

temperature characteristics

As described in the classification of ceramic capacitors, the capacitance of high dielectric constant type capacitors changes depending on the temperature of use. For example, the standard states that the X7R characteristic should be within ± 15% in the operating temperature range, but it is necessary to know the actual amount of change.

Figure 4 is a typical example of temperature characteristics.

Fig. 5: Representative example of temperature characteristics

From the website of Wurth Elektronik

From this example, it can be seen that the X7R has the characteristic that there are few temperatures where the capacity becomes positive in the operating temperature range, and the capacity decreases compared to normal temperature in the low and high temperature range.

change over time

Ceramic capacitors with a high dielectric constant also change over time.

Figure 6 is a representative example of changes over time. You can see that the capacity has decreased over time.

Figure 6: Representative example of change over time

From the website of Wurth Elektronik

From the graph, the relationship between time and capacity change decreases almost linearly in a semi-logarithmic graph where time is logarithmically.

Information on simulation tools

Please click the image above. Link to the simulation tool "RED EXPERT" page.

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