Ⅰ. What is a mica capacitor?
Ⅱ. The structure of mica capacitor
Ⅲ. Characteristics of mica capacitors
Ⅳ. The classification of mica capacitors
Ⅴ. How to choose mica capacitor?
Ⅵ. Basic parameters of mica capacitors
Ⅶ. The difference between mica capacitors and general capacitors
Ⅷ. The application of mica capacitor
Ⅰ. What is a mica capacitor?
Mica Capacitors are electrode plates made of metal foil or sprayed with silver on mica sheets. After the electrode plates and mica are laminated layer by layer, they are then die-cast in bakelite powder or sealed in epoxy resin capacitor. Mica is a natural dielectric with the highest dielectric constant. Because mica is brittle and cannot be wound, it can only be manufactured by lamination when it wants to increase the capacity, so it is also called stuck mica capacitors. Its shape is mostly square. Capacitors made of mica have the advantages of excellent insulation resistance, small dielectric loss, good frequency characteristics and temperature characteristics, small temperature coefficient, and high capacity accuracy.
Mica capacitors include two forms: stacked-foil and silver mica form. The capacitance range of mica capacitors is usually 10~68000pF, the rated voltage is 100V~7kV, the temperature coefficient is between -20~+100ppm/℃, and the dielectric constant is generally 5. Mica capacitors are suitable for broadcasting and television products, DC, AC and pulsating circuits with high requirements for various instruments and communication equipment.
Ⅱ. The structure of mica capacitor
The capacitor structure is relatively simple. Previous mica capacitors were coated with a thin silver sheet on a thin mica sheet. Although electrons are added, there is almost no air gap between the two layers due to physical imperfections, which affects the accuracy of clamped mica capacitors. Additionally, these gaps can cause problems due to mechanical stress and capacitance changes over time.
Silver mica capacitors after World War II cover silver directly on the outside of the mica and then encapsulate it. The capacitance of silver mica capacitors is relatively small, ranging from a few pF to several nF, and the largest can reach 1 microfarad, but it is not common. Silver mica capacitors are usually rated between 100 and 1000 volts, but there are also special high voltage mica capacitors designed for RF TX rated up to 10 kV.
Ⅲ. Characteristics of mica capacitors
Mica capacitors have the following characteristics:
1. The price is more expensive. In recent years it has been gradually replaced by ceramic capacitors and organic film capacitors.
2. The inherent inductance is small, not easy to age, and the frequency characteristics are stable. It is one of the high-frequency capacitors with excellent performance.
3. Its capacity range is not wide, generally between 10-51000pF.
4. High insulation resistance, generally up to 1000-7500MΩ.
5. The dielectric loss is small. Mica capacitors use mica flakes as the medium, which has a high dielectric constant and low dielectric loss. The dielectric constant reflects the ability of a medium to store electrical energy. The high dielectric constant of mica flakes enables mica capacitors to store more electrical energy. And the low dielectric loss indicates that the mica capacitor can effectively maintain the stability of electric energy during the working process.
6. The temperature characteristics are good, and the operating environment temperature is generally within the range of -55°C ~ +85°C.
7. Mica capacitors have good stability and can maintain a relatively stable capacitance value in long-term use. This is because mica flakes have high mechanical strength, are not easily affected by external factors, and can work stably for a long time.
8. The structure of the mica capacitor is mainly composed of a layer of mica sheet sandwiched between two metal foils. Mica flakes are an insulating material with good insulating properties and mechanical strength. Therefore, it can effectively isolate the metal foil and prevent the occurrence of short circuit and leakage.
Ⅳ. The classification of mica capacitors
It prints asymmetric electrodes on both sides of the silver mica sheet and extends to the end face, and the two ends of the core stack laminate are soldered with silver to lead out wires.
2. Clamp Type Compression Molded Mica Capacitor
The upper and lower layers of the core group are protective sheets, and the middle is silver mica sheets and lead-out foils interlaced between each layer of mica sheets. The stacked core group is drawn out by bending the foil, wrapping and fixing the core group, and then the two ends of the clip are installed with the outer leads, that is, the two electrodes of the capacitor, and finally the bakelite shell is sealed.
There are button type, button monolithic type and other types of through-heart mica capacitors. The electrodes are drawn out from the center and the outer circle, and finally a protective layer is added outside the core group.
Silver mica capacitors are made by directly plating a layer of silver on the surface of mica. The silver mica capacitors are then layered until the desired capacitance level is achieved. Once the correct number of layers are added, the electrodes are added, and the capacitor is encapsulated within the resin. Epoxy or ceramic resins tend to be the most commonly used materials for the outer body of a capacitor. We use enclosures to protect silver mica capacitors from environmental elements that can damage the capacitors.
Clamped mica capacitors are made by clamping sheets of mica. The mica sheets are topped with thin silver sheets, and once they are sandwiched together, the electrodes are added. The reason we don't use clamped mica capacitors is that both the mica layer and the silver layer usually have some physical imperfections that would allow air gaps, making them imprecise and unreliable parts.
Ⅴ. How to choose mica capacitor?
1. Frequency response: The frequency response of mica capacitors is also an important indicator. We need to make a selection based on the circuit operating frequency.
2. Size: The size of the mica capacitor is also a factor to consider. We need to choose based on circuit design and various size constraints like width, height, length, etc.
3. Voltage level: Mica capacitors can withstand a wide range of voltage levels, ranging from tens of volts to thousands of volts. We need to choose according to circuit requirements and maximum operating voltage.
4. Operating temperature range: The temperature coefficient of mica capacitors is small, and the performance is stable in a wide temperature range. We need to choose according to the working environment and temperature requirements.
5. Capacitance value: Determine the required capacitance value according to the needs of circuit design. Generally speaking, the capacity of mica capacitors ranges from tens of picofarads to hundreds of microfarads, and we need to choose according to the needs of the circuit.
When choosing mica capacitors, we need to consider multiple factors comprehensively. First of all, circuit design and circuit parameters are the key factors that determine the selection of capacitors. Mica capacitors are characterized by high stability and high voltage resistance, and are suitable for high-precision circuit design. In addition, the working environment is also a factor to consider. For example, if the temperature of the working environment changes greatly, then we need to choose a mica capacitor with a wider temperature range. In addition, the supplier's brand and quality assurance are also factors that need to be considered when selecting mica capacitors. A reputable supplier can provide high-quality, reliable mica capacitors to ensure circuit stability and reliability. When choosing a mica capacitor, we need to consider various requirements, including circuit design, circuit parameters, working environment, and supplier's brand and quality assurance, in order to make a suitable choice.
Ⅵ. Basic parameters of mica capacitors
1. Capacitance
The test conditions for the capacitance of mica capacitors are: the test frequency for capacitance below 1000pF is 1MHz, and the test frequency for capacitance greater than 1000pF is 1KHz. The capacitance tolerance of mica capacitors can be very low, reaching 0.1%. The general capacitor tolerance is mostly 10% or 20%, less than 5%. The tolerance of mica capacitors can be so tight, which shows that the stability of mica capacitors is very good. It varies very little with temperature and time.
2. Current characteristics
The current characteristic of mica capacitors is one of the most notable characteristics of mica capacitors. We can often see in the data of mica capacitors, the dµ/dt parameter that reflects the peak current handling capacity of the capacitor. The dµ/dt of mica capacitors can reach more than 100000V/µs; the corresponding current of 1000pF capacitance under the action of 100000V/µs voltage change rate is 100A. This is what other dielectric capacitors cannot.
Mica capacitors are usually marked with their allowable RMS current in high frequency power applications. Take the domestic CYG-9 type high-power mica capacitor as an example, the rated voltage is 7.5kV, and the nominal capacitor is 0.1μF. The operating current is 57A at 1MHz frequency, and the current is 80.5A for 5min at 1MHz frequency.
3. Voltage characteristics
Mica capacitors have the same voltage rating as other dielectric capacitors. Since the mica capacitor can have a very high operating frequency, the heat generated by the current will be the main factor limiting the mica capacitor. Therefore, the actual AC working voltage of the mica capacitor is lower than the AC RMS rated voltage converted from the DC rated voltage.
Ⅶ. The difference between mica capacitors and general capacitors
1. Small change in capacity
The capacity change of mica capacitor is small. The long-term storage of mica capacitance changes between 0.01% and 0.02%, which is better than ordinary capacitors.
2. Great use
In high-quality, high-precision, high-stability analog circuits, we often see mica capacitors. Mica capacitors are the best choice in high-precision analog circuits. In high-end circuits, such as high-end Hi-Fi audio circuits, the capacitors generally used are mica capacitors.
3. High price
The price of mica capacitors is higher than that of ordinary capacitors. This is because the production process of mica capacitors is complicated, the cost is high, the volume is large, and the capacity is limited.
4. High temperature resistance
In a high temperature environment, mica capacitors can work normally and stably. Its maximum ambient temperature can reach 460°C, far exceeding that of ordinary ceramic capacitors. General aluminum electrolytic capacitors can only work at 105°C.
5. Small temperature coefficient
The temperature coefficient of mica capacitance is small, generally within 1*10^(-6)/℃, which is much better than ordinary organic film capacitors (such as polyester capacitors). Compared with ceramic capacitors, it has great advantages.
Ⅷ. The application of mica capacitor
1. High temperature environment: Mica capacitors can work at relatively high temperatures, so they are often used in aerospace, automotive electronics, industrial control and other fields.
2. High voltage application: Mica capacitors are designed to support relatively high operating voltage, so it is used in power circuits.
3. High-precision applications: Since mica capacitors have high stability and low drift characteristics, they are suitable for circuits that require high-precision capacitance values, such as precision measuring equipment and calibration instruments.
4. Pulse tolerance: Mica capacitors have good tolerance to pulse signals, so it is suitable for pulse circuits and equipment, such as laser drive circuits, pulse generators, etc.
5. Signal coupling and coupling winding: In signal coupling circuits, mica capacitors transfer signals from one part to another and isolate them at the same time. This is common in amplifier and filter design.
6. DC coupling and winding: Mica capacitors are used in DC coupling circuits to block DC signals while allowing AC signals to pass through. Additionally, they are also used in the windings of inductors for building filters and resonant circuits.
7. In the circuit
(1) For resonant circuit
A resonant circuit is a circuit used to adjust the frequency in a circuit. Mica capacitors can be used in resonant circuits to adjust the frequency in the circuit, thereby realizing the resonance of the circuit.
(2) For coupling circuit
A coupled circuit is a method used to pass a signal from one circuit to another. Mica capacitors can be used in coupling circuits to transmit signals in the circuit, so as to realize the connection between different circuits.
(3) For high frequency circuit
Mica capacitors have excellent high-frequency performance and are suitable for use in radio frequency (RF) circuits, such as wireless communication equipment, radar systems, etc. In these applications, stability and low loss are key elements.
(4) Used in filter circuit
In the circuit, the mica capacitor can be used as a capacitor in the filter circuit to filter the high-frequency noise and clutter signals in the circuit, making the signal in the circuit more pure and stable.
