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The role of ceramic capacitors in switching power adapters
Ceramic capacitors have the advantages of long life, high operating frequency, and small size. They are widely used in switching power adapters. Ceramic capacitors are also called ceramic dielectric capacitors. Their dielectric is a natural material ceramic. Ceramic capacitors have a variety of structural forms, and their principles are roughly the same. They are mainly based on the physical and chemical properties of ceramics to strictly control the thickness, area, smoothness and flatness of the ceramic sheet, and then finely processed by modern technology. There are many types of ceramics. According to different components, they can be divided into titanium ceramics, thermal ceramics and barium titanate ceramics. Titanium ceramics have a higher dielectric constant and a negative temperature coefficient. Thermal ceramics have a lower dielectric constant, a smaller negative temperature coefficient, and good capacitance stability. Barium titanate materials have the highest dielectric constant and a large temperature coefficient. The stability of the capacitor is very poor. Generally, high-tech electronic products do not use this type of capacitor. Ceramic capacitors are often used to suppress common-mode noise in switching power adapter circuits. They are often connected between the circuit and the ground, such as Y capacitors.
1. Characteristics of ceramic capacitors:
1) Ceramic capacitors have strong adaptability to the working environment and are resistant to acid, alkali and salt. Even if they are corroded by salt water or corrosive air, they can still work normally for a long time and are not easy to age.
2) The dielectric constant of ceramic materials is very large, generally ranging from tens of picofarads to hundreds of picofarads, and some have dielectric constants as high as thousands of picofarads. This makes the volume of ceramic capacitors very small. If multiple layers are used, the capacity of the capacitor can be greatly expanded.
3) The structure is simple, the processing and production technology requirements are not high, the raw materials are abundant and the price is cheap.
4) The capacitor has strong insulation performance and high insulation resistance, and can be made into a very high voltage capacitor, which can withstand voltages up to 2kV.
5) The ceramic dielectric material of ceramic capacitors cannot be curled, and the capacitor itself has no inductance. The ceramic capacitors produced in this way have high high-frequency characteristics and are widely used in aerospace, communications, switching power supply adapters and other fields.
6) It has good heat resistance and high temperature resistance, and can work normally and stably under conditions up to 500~600℃.
7) The temperature coefficient range is very wide, and capacitors with different temperature coefficients can be produced to suit different occasions.
8) The loss tangent of ceramic capacitors has little relationship with frequency, and the loss value does not increase with the increase of frequency. However, its mechanical strength is low and it is easy to break and damage.
1. The role of ceramic capacitors in switching power adapters:
Generally speaking, capacitors can block DC signals and transmit AC signals. They play a very important role in preventing and filtering noise, high-frequency electromagnetic interference and stabilizing electrical performance. Ceramic capacitors play the following roles in the electronic circuits of switching power adapters:
1. Smooth ripple current. The power conversion circuit in the switching power supply adapter outputs electrical energy in pulsating direct current with large current ripple. Switching circuits often use electrolytic capacitors with large capacitance. With the high frequency and miniaturization of switching power supplies, the requirements for power output parameters are getting higher and higher. At present, multilayer ceramic capacitors are used. This capacitor uses nickel inside, and after carbon film high temperature treatment, the capacitance, voltage resistance level and leakage current are greatly improved. Compared with aluminum electrolytic capacitors, the capacitive reactance of multilayer ceramic capacitors is much smaller, and the effect of smoothing ripple in circuits is very good. The capacitance of the capacitor itself is very low, and the smoothness of the output ripple current of 100~500kHz is significantly improved. Generally speaking, as the use time of aluminum electrolytic capacitors increases, its capacitance decreases as the electrolyte dries up, while the capacitance of ceramic capacitors hardly changes with time.
2. Absorb surge voltage. During the operation of electronic circuits, due to the influence of environmental conditions, traction load, sudden changes in circuit components, etc., surge voltage occurs under the action of transformer inductance. This surge voltage has a high amplitude and large energy, which will be fatal to the driving power transistor of the switching power supply. In order to protect the safety of the transistor, ceramic capacitors and resistors are often connected in series and connected to the primary winding of the transformer to form an absorption circuit. The capacitor is generally below 470pF and the withstand voltage is above 630V.
3. Bypass noise interference. In order to prevent noise from entering the load from the output circuit or low-frequency electromagnetic waves from the input circuit into the power supply, ceramic capacitors are generally connected to the circuit to suppress normal noise and for low-pass filtering. This kind of capacitor is called a bypass capacitor, which is connected to the output circuit of the main circuit and has a better bypass effect. The capacitance of this capacitor is generally 220~3300pF, and the withstand voltage range depends on the circuit function, generally 500V~1.2kV.
4. Filter out noise. The input circuit of the switching power adapter is often connected to an AC circuit filter, which is used to filter out the external noise and the internal noise. The capacitors used to filter out noise are all ceramic capacitors. The capacitor connected to the power supply line has a lower frequency of suppressing noise, requires a larger capacitance, and has a withstand voltage of 275V. It is called an X capacitor.
The role of ceramic capacitors in switching power adapters
Ceramic capacitors have the advantages of long life, high operating frequency, and small size. They are widely used in switching power adapters. Ceramic capacitors are also called ceramic dielectric capacitors. Their dielectric is a natural material ceramic. Ceramic capacitors have a variety of structural forms, and their principles are roughly the same. They are mainly based on the physical and chemical properties of ceramics to strictly control the thickness, area, smoothness and flatness of the ceramic sheet, and then finely processed by modern technology. There are many types of ceramics. According to different components, they can be divided into titanium ceramics, thermal ceramics and barium titanate ceramics. Titanium ceramics have a higher dielectric constant and a negative temperature coefficient. Thermal ceramics have a lower dielectric constant, a smaller negative temperature coefficient, and good capacitance stability. Barium titanate materials have the highest dielectric constant and a large temperature coefficient. The stability of the capacitor is very poor. Generally, high-tech electronic products do not use this type of capacitor. Ceramic capacitors are often used to suppress common-mode noise in switching power adapter circuits. They are often connected between the circuit and the ground, such as Y capacitors.
1. Characteristics of ceramic capacitors:
1) Ceramic capacitors have strong adaptability to the working environment and are resistant to acid, alkali and salt. Even if they are corroded by salt water or corrosive air, they can still work normally for a long time and are not easy to age.
2) The dielectric constant of ceramic materials is very large, generally ranging from tens of picofarads to hundreds of picofarads, and some have dielectric constants as high as thousands of picofarads. This makes the volume of ceramic capacitors very small. If multiple layers are used, the capacity of the capacitor can be greatly expanded.
3) The structure is simple, the processing and production technology requirements are not high, the raw materials are abundant and the price is cheap.
4) The capacitor has strong insulation performance and high insulation resistance, and can be made into a very high voltage capacitor, which can withstand voltages up to 2kV.
5) The ceramic dielectric material of ceramic capacitors cannot be curled, and the capacitor itself has no inductance. The ceramic capacitors produced in this way have high high-frequency characteristics and are widely used in aerospace, communications, switching power supply adapters and other fields.
6) It has good heat resistance and high temperature resistance, and can work normally and stably under conditions up to 500~600℃.
7) The temperature coefficient range is very wide, and capacitors with different temperature coefficients can be produced to suit different occasions.
8) The loss tangent of ceramic capacitors has little relationship with frequency, and the loss value does not increase with the increase of frequency. However, its mechanical strength is low and it is easy to break and damage.
1. The role of ceramic capacitors in switching power adapters:
Generally speaking, capacitors can block DC signals and transmit AC signals. They play a very important role in preventing and filtering noise, high-frequency electromagnetic interference and stabilizing electrical performance. Ceramic capacitors play the following roles in the electronic circuits of switching power adapters:
1. Smooth ripple current. The power conversion circuit in the switching power supply adapter outputs electrical energy in pulsating direct current with large current ripple. Switching circuits often use electrolytic capacitors with large capacitance. With the high frequency and miniaturization of switching power supplies, the requirements for power output parameters are getting higher and higher. At present, multilayer ceramic capacitors are used. This capacitor uses nickel inside, and after carbon film high temperature treatment, the capacitance, voltage resistance level and leakage current are greatly improved. Compared with aluminum electrolytic capacitors, the capacitive reactance of multilayer ceramic capacitors is much smaller, and the effect of smoothing ripple in circuits is very good. The capacitance of the capacitor itself is very low, and the smoothness of the output ripple current of 100~500kHz is significantly improved. Generally speaking, as the use time of aluminum electrolytic capacitors increases, its capacitance decreases as the electrolyte dries up, while the capacitance of ceramic capacitors hardly changes with time.
2. Absorb surge voltage. During the operation of electronic circuits, due to the influence of environmental conditions, traction load, sudden changes in circuit components, etc., surge voltage occurs under the action of transformer inductance. This surge voltage has a high amplitude and large energy, which will be fatal to the driving power transistor of the switching power supply. In order to protect the safety of the transistor, ceramic capacitors and resistors are often connected in series and connected to the primary winding of the transformer to form an absorption circuit. The capacitor is generally below 470pF and the withstand voltage is above 630V.
3. Bypass noise interference. In order to prevent noise from entering the load from the output circuit or low-frequency electromagnetic waves from the input circuit into the power supply, ceramic capacitors are generally connected to the circuit to suppress normal noise and for low-pass filtering. This kind of capacitor is called a bypass capacitor, which is connected to the output circuit of the main circuit and has a better bypass effect. The capacitance of this capacitor is generally 220~3300pF, and the withstand voltage range depends on the circuit function, generally 500V~1.2kV.
4. Filter out noise. The input circuit of the switching power adapter is often connected to an AC circuit filter, which is used to filter out the external noise and the internal noise. The capacitors used to filter out noise are all ceramic capacitors. The capacitor connected to the power supply line has a lower frequency of suppressing noise, requires a larger capacitance, and has a withstand voltage of 275V. It is called an X capacitor.