Characteristics and selection of ceramic capacitors

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Time of issue:2020-04-09 14:26
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(Summary description)Ceramic capacitors are currently the most widely used capacitors in electronic equipment, accounting for about 50% of the total number of capacitors used. However, due to the lack of understanding of their characteristics by many people, they lack due attention in use. In order to meet the standardization and standardization requirements of use, the following is an overview of the characteristics of ceramic capacitors and the matters needing attention in use: 1. Characteristic classification of ceramic capacitors: Ceramic capacitors have the advantages of good heat resistance, excellent insulation, simple structure, and low price. However, the characteristics of different ceramic materials are very different and must be selected correctly according to the requirements of use. Ceramic capacitors are classified into high-frequency ceramic capacitors (Class 1 ceramic) and low-frequency ceramic capacitors (Class 2 ceramic) according to frequency characteristics; high-voltage ceramic capacitors (above 1KVDC) and low-voltage ceramic capacitors (below 500VDC) , Are described as follows: 1. High-frequency ceramic capacitors (also known as Class 1 ceramic capacitors) The loss of this type of ceramic capacitor varies little with frequency in a wide range, and the high-frequency loss value is very small (tanδ≤0.15%, f=1MHz), and the maximum operating frequency can reach more than 1000MHz. At the same time, this type of ceramic capacitor has excellent temperature characteristics and is suitable for high-frequency resonance, filtering and temperature compensation circuits that require high capacity and stability. The national standard models are CC1 (low pressure) and CC81 (high pressure). At present, the commonly used temperature characteristic groups of our company are CH (NP0) and SL groups. The normal capacity ranges are as follows: The temperature coefficient αC=1/C (C2-C1/t2-t1) X106 (PPM/°C) in the table refers to the relative change rate of capacitance for every 1°C temperature change within the allowable temperature range. It can be seen from the above table that the temperature coefficient of the type 1 ceramic dielectric capacitor is very small, especially the CH characteristic, so the CH capacitance of the type 1 ceramic dielectric capacitor is often called a temperature compensation capacitor. However, due to the low dielectric constant of this type of ceramic material, its capacity value is difficult to increase. Therefore, when a capacitor with a higher capacitance value is needed, it can only be found in the 2 types of ceramic dielectric capacitors described below. 2. Low-frequency ceramic capacitors (also known as Class 2 ceramic capacitors) The ceramic material of this type of ceramic dielectric capacitor has a large dielectric constant, so the capacitor is small in size and wide in capacity, but the frequency and temperature characteristics are poor, so it is only suitable for those with low requirements for capacity, loss and temperature characteristics. The low frequency circuit is used as bypass, coupling, filtering and other circuits. The national standard models are CT1 (low pressure) and CT81 (high pressure), and their common temperature characteristic groups and normal capacity ranges correspond to the following: The temperature change rate rC/C in the table refers to the capacity change rate at the upper and lower limit temperature relative to room temperature +25°C. Among them, the 2R group is a low-loss capacitor. Because of its low temperature rise and better frequency characteristics, it can be used in higher frequency applications. For low-voltage ceramic capacitors, when the capacity is greater than 47000pF, you can only choose 3 types of ceramic capacitors (also known as semiconductor ceramic capacitors), for example: 26-ABC104-ZFX, but this type of capacitor has worse temperature characteristics and lower insulation resistance Low, just because of the high dielectric material, the volume can be made small. Therefore, it is only suitable for working circuits with lower requirements. If a larger capacity capacitor is selected, and there are higher requirements for capacity and temperature characteristics, then 27 types of organic film capacitors should be selected. 3. AC ceramic capacitor According to the requirements for the safe use of AC power supply, an AC ceramic capacitor with high insulation characteristics and high dielectric strength has been specially designed and produced in Class 2 ceramic capacitors, also known as Y capacitors, which are divided into Y1, Y2, The three major series of Y3 are classified as follows: 2. The packaging and dimensions of ceramic capacitors. Although ceramic capacitors have many of the above advantages, due to the low mechanical strength and fragility of the ceramic material itself, the geometric size of the wafer is limited. This is also the main reason why different temperature characteristics have different capacity ranges. Generally

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Characteristics and selection of ceramic capacitors

(Summary description)Ceramic capacitors are currently the most widely used capacitors in electronic equipment, accounting for about 50% of the total number of capacitors used. However, due to the lack of understanding of their characteristics by many people, they lack due attention in use. In order to meet the standardization and standardization requirements of use, the following is an overview of the characteristics of ceramic capacitors and the matters needing attention in use:

1. Characteristic classification of ceramic capacitors:

Ceramic capacitors have the advantages of good heat resistance, excellent insulation, simple structure, and low price. However, the characteristics of different ceramic materials are very different and must be selected correctly according to the requirements of use. Ceramic capacitors are classified into high-frequency ceramic capacitors (Class 1 ceramic) and low-frequency ceramic capacitors (Class 2 ceramic) according to frequency characteristics; high-voltage ceramic capacitors (above 1KVDC) and low-voltage ceramic capacitors (below 500VDC) , Are described as follows:

1. High-frequency ceramic capacitors (also known as Class 1 ceramic capacitors)

The loss of this type of ceramic capacitor varies little with frequency in a wide range, and the high-frequency loss value is very small (tanδ≤0.15%, f=1MHz), and the maximum operating frequency can reach more than 1000MHz. At the same time, this type of ceramic capacitor has excellent temperature characteristics and is suitable for high-frequency resonance, filtering and temperature compensation circuits that require high capacity and stability. The national standard models are CC1 (low pressure) and CC81 (high pressure). At present, the commonly used temperature characteristic groups of our company are CH (NP0) and SL groups. The normal capacity ranges are as follows:

The temperature coefficient αC=1/C (C2-C1/t2-t1) X106 (PPM/°C) in the table refers to the relative change rate of capacitance for every 1°C temperature change within the allowable temperature range. It can be seen from the above table that the temperature coefficient of the type 1 ceramic dielectric capacitor is very small, especially the CH characteristic, so the CH capacitance of the type 1 ceramic dielectric capacitor is often called a temperature compensation capacitor. However, due to the low dielectric constant of this type of ceramic material, its capacity value is difficult to increase. Therefore, when a capacitor with a higher capacitance value is needed, it can only be found in the 2 types of ceramic dielectric capacitors described below.

2. Low-frequency ceramic capacitors (also known as Class 2 ceramic capacitors)

The ceramic material of this type of ceramic dielectric capacitor has a large dielectric constant, so the capacitor is small in size and wide in capacity, but the frequency and temperature characteristics are poor, so it is only suitable for those with low requirements for capacity, loss and temperature characteristics. The low frequency circuit is used as bypass, coupling, filtering and other circuits. The national standard models are CT1 (low pressure) and CT81 (high pressure), and their common temperature characteristic groups and normal capacity ranges correspond to the following:

The temperature change rate rC/C in the table refers to the capacity change rate at the upper and lower limit temperature relative to room temperature +25°C. Among them, the 2R group is a low-loss capacitor. Because of its low temperature rise and better frequency characteristics, it can be used in higher frequency applications.

For low-voltage ceramic capacitors, when the capacity is greater than 47000pF, you can only choose 3 types of ceramic capacitors (also known as semiconductor ceramic capacitors), for example: 26-ABC104-ZFX, but this type of capacitor has worse temperature characteristics and lower insulation resistance Low, just because of the high dielectric material, the volume can be made small. Therefore, it is only suitable for working circuits with lower requirements. If a larger capacity capacitor is selected, and there are higher requirements for capacity and temperature characteristics, then 27 types of organic film capacitors should be selected.

3. AC ceramic capacitor

According to the requirements for the safe use of AC power supply, an AC ceramic capacitor with high insulation characteristics and high dielectric strength has been specially designed and produced in Class 2 ceramic capacitors, also known as Y capacitors, which are divided into Y1, Y2, The three major series of Y3 are classified as follows:

2. The packaging and dimensions of ceramic capacitors.

Although ceramic capacitors have many of the above advantages, due to the low mechanical strength and fragility of the ceramic material itself, the geometric size of the wafer is limited. This is also the main reason why different temperature characteristics have different capacity ranges. Generally

Categories:Company news
Author:
Origin:
Time of issue:2020-04-09 14:26
Views:

Ceramic capacitors are currently the most widely used capacitors in electronic equipment, accounting for about 50% of the total number of capacitors used. However, due to the lack of understanding of their characteristics by many people, they lack due attention in use. In order to meet the standardization and standardization requirements of use, the following is an overview of the characteristics of ceramic capacitors and the matters needing attention in use:

1. Characteristic classification of ceramic capacitors:

Ceramic capacitors have the advantages of good heat resistance, excellent insulation, simple structure, and low price. However, the characteristics of different ceramic materials are very different and must be selected correctly according to the requirements of use. Ceramic capacitors are classified into high-frequency ceramic capacitors (Class 1 ceramic) and low-frequency ceramic capacitors (Class 2 ceramic) according to frequency characteristics; high-voltage ceramic capacitors (above 1KVDC) and low-voltage ceramic capacitors (below 500VDC) , Are described as follows:

1. High-frequency ceramic capacitors (also known as Class 1 ceramic capacitors)

The loss of this type of ceramic capacitor varies little with frequency in a wide range, and the high-frequency loss value is very small (tanδ≤0.15%, f=1MHz), and the maximum operating frequency can reach more than 1000MHz. At the same time, this type of ceramic capacitor has excellent temperature characteristics and is suitable for high-frequency resonance, filtering and temperature compensation circuits that require high capacity and stability. The national standard models are CC1 (low pressure) and CC81 (high pressure). At present, the commonly used temperature characteristic groups of our company are CH (NP0) and SL groups. The normal capacity ranges are as follows:

The temperature coefficient αC=1/C (C2-C1/t2-t1) X106 (PPM/°C) in the table refers to the relative change rate of capacitance for every 1°C temperature change within the allowable temperature range. It can be seen from the above table that the temperature coefficient of the type 1 ceramic dielectric capacitor is very small, especially the CH characteristic, so the CH capacitance of the type 1 ceramic dielectric capacitor is often called a temperature compensation capacitor. However, due to the low dielectric constant of this type of ceramic material, its capacity value is difficult to increase. Therefore, when a capacitor with a higher capacitance value is needed, it can only be found in the 2 types of ceramic dielectric capacitors described below.

2. Low-frequency ceramic capacitors (also known as Class 2 ceramic capacitors)

The ceramic material of this type of ceramic dielectric capacitor has a large dielectric constant, so the capacitor is small in size and wide in capacity, but the frequency and temperature characteristics are poor, so it is only suitable for those with low requirements for capacity, loss and temperature characteristics. The low frequency circuit is used as bypass, coupling, filtering and other circuits. The national standard models are CT1 (low pressure) and CT81 (high pressure), and their common temperature characteristic groups and normal capacity ranges correspond to the following:

The temperature change rate rC/C in the table refers to the capacity change rate at the upper and lower limit temperature relative to room temperature +25°C. Among them, the 2R group is a low-loss capacitor. Because of its low temperature rise and better frequency characteristics, it can be used in higher frequency applications.

For low-voltage ceramic capacitors, when the capacity is greater than 47000pF, you can only choose 3 types of ceramic capacitors (also known as semiconductor ceramic capacitors), for example: 26-ABC104-ZFX, but this type of capacitor has worse temperature characteristics and lower insulation resistance Low, just because of the high dielectric material, the volume can be made small. Therefore, it is only suitable for working circuits with lower requirements. If a larger capacity capacitor is selected, and there are higher requirements for capacity and temperature characteristics, then 27 types of organic film capacitors should be selected.

3. AC ceramic capacitor

According to the requirements for the safe use of AC power supply, an AC ceramic capacitor with high insulation characteristics and high dielectric strength has been specially designed and produced in Class 2 ceramic capacitors, also known as Y capacitors, which are divided into Y1, Y2, The three major series of Y3 are classified as follows:

2. The packaging and dimensions of ceramic capacitors.

Although ceramic capacitors have many of the above advantages, due to the low mechanical strength and fragility of the ceramic material itself, the geometric size of the wafer is limited. This is also the main reason why different temperature characteristics have different capacity ranges. Generally, the allowable diameter D≤12mm for low-voltage disc capacitors, and the allowable diameter D≤16mm for high-voltage capacitors. If it exceeds this size, the difficulty of production and processing and the rejection rate will be greatly increased, and the tiny cracks produced on the body of the ceramic will cause great hidden dangers to the reliability of the capacitor. Because different manufacturers have different levels of material development and process manufacturing, their external dimension standards are also different, so their nominal capacity ranges are also partially different. Therefore, the above-mentioned capacity division table is only the result of an industry average. In the future, with the further improvement of material technology, the size of ceramic capacitors will be further reduced, and the capacity range will be further expanded.

The encapsulation forms of disc ceramic capacitors are usually differentiated by voltage. The low-voltage products CC1 and CT1 series below 500VDC are all encapsulated by phenolic resin, which has poor insulation strength and moisture resistance, but lower cost. In order to improve the moisture resistance, the outer layer of such encapsulation is impregnated with a thin layer of wax. Below 1KVDC and AC capacitor series, all are encapsulated with flame-retardant epoxy resin with excellent insulation strength and moisture resistance.

In addition to wafer type ceramic capacitors, there are currently widely used axial lead color ring ceramic capacitors and chip ceramic capacitors. The internal structure of the ceramic capacitor is laminated, so the volume is small, but the capacity can reach more than 1μF. Conducive to assembly, but due to its structural limitations, the insulation resistance and withstand voltage cannot be made very high, so it is currently limited to low voltage (within 50V) products, and its loss and temperature characteristics are the same as wafer capacitors.

Three, the selection of ceramic capacitors and matters needing attention

1. Ensure the versatility and standardization of material selection:

Because different temperature characteristics correspond to different capacity ranges and accuracy standards, the selection must conform to the series standards, and the selection of capacitance values must conform to the E24 (or E96) series values. At present, our company has many P/Ns that violate the reversal standard, such as 26-ABC472-JZX, 28-AB0XXX-JBX, etc. Such problems are mainly caused by the lack of necessary understanding of the temperature characteristics of ceramic capacitors by some designers .

2. The appropriate model should be selected according to the working status and environmental conditions of the line, and its main parameters should meet the requirements of the line.

1) In high-frequency resonant circuits, in addition to the low loss of the capacitor, good temperature stability of the capacitance is also required. Usually, a type 1 ceramic dielectric capacitor is used. The CH characteristic is also called a zero temperature coefficient product, and its capacity basically does not change with temperature Changes, but its capacity is only between a few PF to a few hundred PF.

2) For capacitors for low-frequency coupling, bypassing, and filtering, miniaturization and low cost are the main factors. However, the temperature stability of loss and capacity is not high. Generally, type 2 ceramic capacitors can be selected. It has a wide range of capacity options.

3) Although ceramic capacitors have a larger withstand voltage margin than film capacitors and electrolytic capacitors, they are not allowed to be used under conditions that exceed their rated voltage, otherwise the metal ions in the electrodes will migrate in the ceramic medium under the action of strong electric fields. The speed increases and the insulation resistance of the capacitor decreases, which affects the long-term reliability of the whole machine.

4) For capacitors working under high temperature and high pressure conditions, care should be taken to select products with higher insulation resistance to prevent the capacitor from failing due to a vicious cycle caused by increased leakage. Usually the insulation resistance IR≥10000MΩ. For example: 2KV withstand voltage and low loss products should be used in the filter position of the CRT acceleration pole to reduce the temperature rise and ensure sufficient insulation resistance; for the reverse circuit circuit, because of the high capacity stability and loss requirements, only 1 Class high voltage ceramic capacitors (P/N: 26-AMKXXX-JZX) are used as capacity compensation capacitors for polypropylene capacitors, otherwise they will cause serious quality risks.

In summary, the difference between ceramic capacitors and other capacitors is that ceramic capacitors have many different temperature groups according to different materials, and their characteristics and capacity ranges are very different. If you have a full understanding of this, you can avoid hidden quality hazards caused by improper selection.

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