February 24, 2023
Classification and specification of ceramic capacitors
The ceramic capacitor can be divided into two types according to the dielectric type, namely, Class I ceramic capacitor and Class II ceramic capacitor.
Class I ceramic capacitor, formerly known as high-frequency ceramic capacitor, refers to the capacitor made of ceramic dielectric with low dielectric loss, high insulation resistance and linear change of dielectric constant with temperature. It is especially suitable for resonant circuits and other circuits requiring small loss and stable capacitance, or for temperature compensation.
Class II ceramic capacitor used to be called low frequency ceramic capacitor. It refers to the capacitor using ferroelectric ceramics as the medium, so it is also called ferroelectric ceramic capacitor. This type of capacitor has a large specific capacitance, its capacitance varies nonlinearly with temperature, and its loss is large. It is often used in electronic equipment for bypass, coupling, or other circuits with low requirements for loss and capacitance stability.
Class I ceramic capacitor: according to the American Electrotechnical Association (EIA) standard, it is C0G (the number 0, not the letter O, and some documents have a clerical error of COG) or NP0 (the number 0, not the letter O, and some documents have a clerical error of NPO), as well as China's standard CC series and other models of ceramic media (the temperature coefficient is 0 ± 30PPM/℃).
This medium is extremely stable, with low temperature coefficient and no aging phenomenon. The loss factor is not affected by voltage, frequency, temperature and time. The dielectric coefficient can reach 400 and the dielectric strength is relatively high.
This medium is very suitable for high frequency (especially high frequency power oscillation of industrial high frequency induction heating, high frequency power capacitor of high frequency wireless transmission and other applications), ultra-high frequency and the working environment of timing and oscillation circuit with strict requirements for capacitance and stability.
The only disadvantage of this kind of dielectric capacitor is that the capacitance cannot be very large (due to the relatively small dielectric coefficient). Generally, the capacitance of 1206 surface-mounted C0G dielectric capacitor ranges from 0.5PF to 0.01 μ F。
Class II ceramic capacitor: Class II stable ceramic dielectric materials, such as X7R and X5R of the American Electrotechnical Association (EIA) standard and CT series of the Chinese standard (temperature coefficient is ± 15.0%).
The dielectric coefficient of this medium varies greatly with temperature, and is not suitable for occasions with high temperature coefficient requirements such as timing and oscillation. However, because its dielectric coefficient can be large (up to 1200), its capacitance can be relatively large, and it is suitable for coupling, bypass and filtering with high temperature requirements for working environment (X7R: - 55~+125 ℃).
Generally, the capacitance of 1206 SMD package can reach 10 μ F or higher;
Class II usable ceramic dielectric materials, such as Z5U and Y5V of the American Electrotechnical Association (EIA) standard and low-grade product models of the CT series of China standard (temperature coefficient is+22%, - 56% of Z5U and+22%, - 82% of Y5V).
The dielectric coefficient of this medium varies greatly with temperature, and is not suitable for occasions with high temperature coefficient requirements such as timing and oscillation. However, because its dielectric coefficient can be large (up to 1000~12000), its capacitance can be larger than that, and it is suitable for coupling, bypass and filtering with general working environment temperature requirements (- 25~+85 ℃).
Generally, 1206 surface-mounted Z5U and Y5V dielectric capacitors can even reach 100 μ F. In a sense, it is a powerful competitor to replace tantalum electrolytic capacitors.
Many people think that common ceramic capacitor terms such as C0G, X7R, B5X and Z5U are physical dielectric specifications. Some manufacturers will say something like "X7R dielectric", but this is not accurate. These three letters represent not physical dielectric, but a performance rating. The manufacturer can choose any dielectric formula as long as they meet the performance specifications of these three letters. The ceramic capacitor with the model name C0G or NP0 belongs to Class I, which is very stable and has very low temperature drift, usually lower than 30ppm/℃. The volumetric efficiency of C0G type capacitor is also the lowest.
The key consideration of Class II capacitor is size, and the three-letter numbering method is shown in Table 1.
The most commonly used models in electronic products are X7R and B5X. This name does not represent a specific dielectric, but a specification. Manufacturers can use any structure they want as long as they meet the specifications. For example, the "X7R" specification features: the operating temperature range is - 55~+125 ℃, and the maximum capacitance change is ± 10%.
If C0G capacitor is used everywhere, our life (and our circuit) will become better. The problem is that they are too large to be widely used in most modern applications. Next, we will see the places where other types of "capacitor deteriorate" except C0G type.