High-voltage ceramic capacitors:
Introduction:
High-voltage ceramic capacitors, that is, high-voltage ceramic capacitors used in power systems, are generally used in products such as power system metering, energy storage, and partial voltage. High-voltage ceramic capacitors have been widely used and not light in the LED lamp industry. High-voltage ceramic capacitors are extruded into a tube, wafer or disk using a high dielectric constant capacitor ceramic (barium titanate-titanium oxide). The dielectric is made by plating silver on ceramics as an electrode by the infiltration method.
effect:
High-voltage ceramic capacitors have the characteristics of wear-resistant DC high voltage, and are suitable for high-voltage bypass and coupling circuits. The low-loss high-voltage wafers have low dielectric loss and are particularly suitable for use in television receivers and scanning circuits. As long as the high-voltage ceramic capacitors are targeted at high frequencies, the high-voltage ceramic capacitors depend on what is used, and the typical role can eliminate high-frequency interference. High-voltage ceramic capacitors used in high-power, high-voltage fields require small, high withstand voltage and good frequency characteristics. With the progress of materials, electrodes and manufacturing technology in recent years, the development of high-voltage ceramic capacitors has made great progress and has been widely used. High-voltage ceramic capacitors have become one of the indispensable components of high-power high-voltage electronic products. The use of high-voltage ceramic capacitors is mainly divided into power equipment for power transmission and distribution systems and equipment for processing pulse energy. Because of the special characteristics of the power system: high AC voltage, high frequency, outdoor environment (-40 degrees to +60 degrees), high lightning voltage / current, etc. Has been in a difficult situation: the harsh environment requires capacitors to have super stability, that is, the rate of change is small; at the same time, products such as metering, energy storage, and voltage division require high precision. The partial discharge, that is, the partial discharge volume has extremely strict requirements: the partial discharge is zero.
advantage:
1.Capacity loss has high stability with temperature and frequency
2.Special series structure is suitable for high voltage and extremely long-term working reliability
3. High current climbing rate and suitable for non-inductive structure of high current loop.
difference:
· Comparison of the characteristics of high-voltage ceramic capacitors and high-voltage ceramic capacitors: Features of high-voltage ceramic capacitors 1. No certification required
2. Ultra high voltage can reach 7KV, which is rare at high,
3. Printing method and Y capacitor do not need to put the certification of various countries on the surface of the product.
4 The voltage can be as low as 16V
5, the maximum withstand voltage is 2 times the standard production of 1.5 times the AC breakdown voltage characteristics of type A materials outside the ceramic capacitor encapsulated with epoxy resin breakdown voltage. Relationship with gap length G (difference between wafer radius and electrode radius). The diameter of the capacitor is 18mm, the dielectric constant of the material is 1460 ′ (hereinafter referred to as A material), and the electrode is a silver electrode. The test conditions are 25 ℃, 50Hz AC voltage is applied, and the voltage rise rate is ZkV / s.
Commonly used in high pressure applications.
Ceramics are divided into Type I porcelain, Type II porcelain, and Type III porcelain.
Class I porcelain, NP0, good temperature characteristics, frequency characteristics and voltage characteristics, because the dielectric constant is not high, so the capacity is not large;
Class II porcelain, followed by X7R, has better temperature and voltage characteristics;
Type III porcelain has a high dielectric constant, so the capacity can be made large, but the temperature characteristics and voltage characteristics are not very good.
Ceramic capacitors are generally small.
In addition, another important feature is emphasized:
Porcelain capacitors are often short-circuited after breakdown. (This is its weakness)
When a film capacitor fails, it is generally open.
The functions of high-voltage ceramic capacitors and high-voltage ceramic capacitors are basically the same, and some details will be different. So pay attention to performance when using it.
1. In-line high-voltage ceramic capacitors, commonly known as DIP, are produced from 16VDC to 100KV, but mainly refer to DC and lead type.
Second, there are other types of in-line ceramic capacitors, which are AC ceramic capacitors, which generally refer to 250VAC Y2 safety capacitors and 400VAC Y1 AC safety capacitors. It is obvious from the name that the voltage of this type of capacitor refers to the AC voltage, and it has safety certification from about ten countries. In addition to ceramic capacitors, the voltages of other leaded ceramic capacitors are generally referred to as DC.
Third, SMD ceramic capacitors, commonly known as SMD, the specifications of such capacitors are generally expressed in 0201, 0402, 0603, 0805, 1206, 1210 and so on. . The English abbreviation of chip capacitor is MLCC, and the voltage is from 6.3VDC to 2KV or more. Of course, the higher the voltage, the more expensive it is.
Fourth, bolt-type high-voltage ceramic capacitors. This type of capacitor is generally resistant to very high voltages and is often referred to as AC voltage in power systems. Such as 40KV102K, 40KV103K, 40KV153K, etc., there are many types, but the voltage inside is not DC. Because the electricity used in our homes or factories and enterprises is AC! The technical content of this type of capacitor is quite high. Often, many companies can make this shape, but they still can't make the quality required by customers. The reason is: first of all, this type of product requires high AC voltage, and most of them The factory standard is DC voltage, so it was eliminated in the sample submission stage. Second, this type of high-voltage ceramic capacitor requires ultra-low partial discharge. The larger the partial discharge, the lower the actual withstand voltage of the capacitor. Therefore, Partial discharge is the best standard for measuring the quality of a capacitor; once again, the ultra-high power frequency, the general lead-type capacitors must also achieve a high power frequency, and this bolt type has higher requirements. Finally, this type of capacitor has strict requirements on the material, because the loss and temperature coefficient of different materials and the dielectric coefficient are different.
High-voltage ceramic capacitors
High-voltage generators use many high-voltage ceramic capacitors and large-capacity high-voltage capacitors. Traditionally, customers generally use high-voltage film capacitors, but as the advantages of ceramic capacitors continue to manifest, in the future, film capacitors will appear less and less in high-voltage generators.
The advantages and disadvantages of high-voltage film capacitors and high-voltage ceramic capacitors are mainly the following:
1. The service life of high-voltage ceramic capacitors is longer. The life of film capacitors is three or two years, and electrical products will not exceed five years. The high-voltage ceramic capacitors are different, and they are normally used for 5 to 10 years.
2. The internal resistance of the high-voltage ceramic capacitor is smaller. This is determined by their respective structural characteristics. The internal resistance of high-voltage ceramic capacitors is very small, and the film capacitor is wound because of the winding method. Another negative effect of this large internal resistance is that the capacitor will continue to increase in the process of repeated charging and discharging of the capacitor, and will cause the capacitor to fail in the circuit at a certain time.
3. Relatively speaking, the voltage of high-voltage ceramic capacitors is higher. Relatively speaking, the capacitance of film capacitors is not as high as that of ceramic capacitors. This is a consensus;
4. There are advantages and disadvantages. The capacity of ceramic capacitors is small.
High-voltage ceramic capacitors, test methods
The reliability test of high-voltage ceramic capacitors, also called aging test, life test, includes many aspects of test content:
1, series resistance test, insulation resistance test;
2, tensile test, that is, the firmness of the lead and chip welding;
3. Positive and negative temperature change rate test, that is, the rate of change of capacitance under the condition of -40 degrees to +60 degrees;
4, aging test, high voltage ceramic capacitors operate for 30 to 60 days under simulated working environment conditions, and test their attenuation and changes in various parameters;
5. Withstand voltage test, including 24 hours working test of rated working voltage; also includes breakdown withstand voltage, that is, destructive test. The critical voltage before the capacitor is broken down is the breakdown voltage.
6, partial discharge test, that is, partial discharge test;
7, life test, that is, based on the aging test, and then perform a fast charge and discharge test on the capacitor under high-frequency impulse current, the number of charge and discharge times is the charge and discharge life. Note that this life is derived from long-term aging It came after.
High-voltage ceramic capacitors, self-recovery period
High-temperature sintering is one of the most important processes for high-voltage ceramic capacitors. After one hundred tons of stamping and casting, and high temperature sintering of more than one thousand degrees, the inside of the chip of the high-voltage ceramic capacitor is structured as a crystal structure. The next 6 hours of high temperature baking and 7 hours of heat preservation completely disrupted the internal structure of the crystal.
Then, in order to restore the structure of the chip and stabilize the characteristics of the chip, high-voltage ceramic capacitors need time to recover. Natural recovery (storage at room temperature) is preferred over 60 days. In addition, products that have been stored for one year and two years have performed well for a long time. Therefore, a long recovery period is of great help to the performance of the capacitor. Without a recovery period of the capacitor, its withstand voltage and current resistance are poor. It has been found through experiments that high-voltage ceramic capacitors with a long storage time will have smaller loss angles and better high-frequency characteristics.
High-voltage ceramic capacitors, units and symbols
· The basic unit of capacitor is: F (method), in addition there are μF (micro method), pF (pico method), and there is a less used unit, that is: nF, because the capacity of capacitor F is very large , So we generally see units of μF, nF, pF, not F units. The specific conversion between them is as follows:
1F = 1000000μF
1μF = 1000nF = 1000000pF
· Symbol of capacitance:
The symbol of the capacitor is also divided into the domestic standard notation and the international electronic symbol notation, but the capacitor symbol is similar in domestic and international. The only difference is that with polar capacitors, the domestic is a horizontal line under an empty basket. , And the international one is a common capacitor plus a "+" symbol to represent the positive electrode.
High-voltage ceramic capacitors
1. When using a DC rated voltage capacitor in an AC circuit or ripple current circuit, be sure to maintain the Vp-p value of the applied voltage or the Vo-p value including the DC bias voltage within the rated voltage range. Applying voltage to the circuit may cause temporary abnormal voltages due to resonance or switching when starting or stopping. Be sure to use capacitors that include these abnormal voltages in the rated voltage range.
2. Working temperature and self-generated heat (suitable for B / E / F characteristics) The surface temperature of the capacitor should be kept below the upper limit of its rated operating temperature range. It is necessary to consider the self-generated heat of the capacitor. The capacitor is at high frequency current, impulse current Self-generated heat may be generated due to dielectric loss during use. The applied voltage should be such that the load such as self-generated heat does not exceed the range of 20 ° C under the ambient temperature of 25 ° C. When measuring, use a thermocouple (K) with a small thermal capacity of 0.1mm And the capacitor should not be affected by the heat dissipation of other components or ambient temperature fluctuations. Overheating may cause the capacitor characteristics and reliability to decrease. (Never measure while the cooling fan is running. Otherwise the accuracy of the measurement data cannot be guaranteed)
3. Test conditions for withstand voltage
(1) Test equipment
AC withstand voltage test equipment should be capable of producing a performance similar to a 50 / 60Hz sine wave.
If a deformed sine wave or an overload voltage exceeding the specified voltage value is applied, it may cause a malfunction.
(2) Voltage application method
When the withstand voltage is applied, the lead or terminal of the capacitor should be firmly connected to the output of the withstand voltage test equipment; then increase the voltage from near zero to the test voltage. If the test voltage does not gradually increase from near zero, it is directly applied to the capacitor , The zero crossing should be included in the application *. At the end of the test, the test voltage should drop to near zero; then the capacitor leads or terminals should be removed from the output of the withstand voltage test equipment. If the test voltage does not gradually increase from near zero, If it is directly applied to the capacitor, a surge voltage may occur, which may cause a failure. 0V voltage sine wave * The zero crossing point refers to the position where the voltage sine passes through 0V.
4. Fail-safe
When the capacitor is damaged, failure may cause a short circuit. In order to avoid dangerous situations such as electric shock, smoke, fire, etc. during the short circuit, please use fuses and other components in the circuit to set the fail-safe function.
Ignoring the above warnings when using this product may cause short circuits in severe cases and cause smoke or local dispersion.
Use and storage environment
(1) The insulating layer of the capacitor does not have a good sealing effect; therefore, do not store the capacitor in corrosive gas, especially in the place where chlorine gas, sulfur gas, acid, alkali, salt, etc. are present, and it should be protected from moisture.
(2) The capacitor should be stored in a place where the temperature and relative humidity do not exceed -10 to 40 ° C and 15 to 85% respectively.
