OFweek semiconductor lighting network with map
Capacitor characteristics (straight through)
A capacitor is a container that can store electrical charge. It consists of two pieces of metal that are closer together, separated by an insulating material. A wide variety of capacitors can be made depending on the insulating material. Such as: mica, porcelain, paper, electrolytic capacitors, etc. In terms of construction, it is further divided into a fixed capacitor and a variable capacitor. The capacitor has infinite DC resistance, that is, the capacitor has a DC blocking effect. The resistance of the capacitor to the alternating current is affected by the alternating current frequency, that is, the capacitor of the same capacity exhibits different capacitive reactance to the alternating current of different frequencies. What will happen to this? This is because the capacitor operates on its charge and discharge function, and the power switch s is not closed. The two metal plates of the capacitor and other common metal plates are uncharged. When the switch S is closed, the free electrons on the positive plate of the capacitor are attracted by the power source and pushed onto the negative plate. Since the capacitor plates are separated by an insulating material, free electrons running from the positive plate are deposited on the negative plate. The positive electrode plate is positively charged due to the reduction of electrons, and the negative electrode plate is negatively charged due to the gradual increase of electrons.
There is a potential difference between the two plates of the capacitor. When this potential difference is equal to the supply voltage, the charging of the capacitor is stopped. At this time, if the power is turned off, the capacitor can still maintain the charging voltage. For a charged capacitor, if we connect the two plates with wires, due to the potential difference between the plates, the electrons will pass through the wires and return to the positive plate until the potential difference between the plates is zero. The capacitor is restored to an uncharged neutral state and there is no current in the conductor. The frequency of the alternating current applied to the two plates of the capacitor is high, and the number of times of charging and discharging of the capacitor is increased; the charging and discharging current is also enhanced; that is, the blocking effect of the capacitor on the alternating current with high frequency is reduced, that is, the capacitive reactance is small, and vice versa. Capacitors have a large capacitive reactance to low frequency AC power. For alternating current at the same frequency. The larger the capacity of the capacitor, the smaller the capacitive reactance, and the smaller the capacity, the larger the capacitive reactance.
Capacitor parameters and classification
In electronic products, capacitors are indispensable electronic devices, which act as smoothing filters for rectifiers, decoupling of power supplies, bypassing of AC signals, and AC coupling of AC and DC circuits in electronic equipment. Due to the variety of types and types of capacitors, we need to understand not only the performance specifications and general characteristics of various types of capacitors, but also the advantages and disadvantages of various components for a given application, as well as mechanical or environmental constraints. . The main parameters of the capacitor and its application will be briefly explained here.
1. Nominal capacitance (CR). Capacitance value indicated by the capacitor product. Mica and ceramic dielectric capacitors have low capacitance (approximately 5000 pF or less); paper, plastic, and some ceramic dielectric capacitors are centered (approximately 0.005 uF to 1.0 uF); typically electrolytic capacitors have larger capacities. This is a rough classification.
2. Category temperature range. The ambient temperature range determined by the capacitor design for continuous operation. This range depends on the temperature limits of its respective category, such as the upper category temperature, the lower category temperature, the rated temperature (the highest ambient temperature at which the rated voltage can be continuously applied), and the like.
3. Rated voltage (UR). At any temperature between the lower category temperature and the rated temperature, the maximum DC voltage or the maximum value of the maximum AC voltage or the peak value of the pulse voltage may be continuously applied to the capacitor. When capacitors are used in high voltage fields, attention must be paid to the effects of corona. Corona is caused by the presence of a gap between the dielectric/electrode layers, which can cause breakdown of the capacitor dielectric in addition to spurious signals that can damage the device. Corona is particularly prone to occur under alternating or pulsating conditions. For all capacitors, ensure that the sum of the DC voltage and the AC peak voltage does not exceed the rated voltage of the capacitor.
4. Loss tangent (tg δ ). At a sinusoidal voltage of a specified frequency, the power loss of the capacitor divided by the reactive power of the capacitor is the loss tangent. In practical applications, the capacitor is not a pure capacitor, and there is an equivalent resistance inside. Its simplified equivalent circuit is shown in the drawing. For electronic equipment, the smaller the RS, the better, that is, the required power loss is small, and the angle between the power and the power of the capacitor is small.
5. Temperature characteristics of the capacitor. It is usually expressed as a percentage of the capacitance at the reference temperature of 20 °C and the capacitance of the relevant temperature.
6. Service life. The life of a capacitor decreases with increasing temperature. The main reason is that the temperature accelerates the chemical reaction and the medium degrades over time.
7. Insulation resistance. As the temperature rise causes an increase in electronic activity, an increase in temperature will lower the insulation resistance. Capacitors include two types of fixed capacitors and variable capacitors. The fixed capacitors can be divided into mica capacitors, ceramic capacitors, paper/plastic film capacitors according to their dielectric materials.
Capacitor categories and symbols
There are also many types of capacitors. In order to distinguish them, several Latin letters are often used to indicate the type of capacitor. The first letter C indicates the capacitance, the second letter indicates the dielectric material, and the third letter indicates the shape, structure, and the like.
Discrimination of the polarity of electrolytic capacitor
Electrolytic capacitors that do not know polarity can be measured for their polarity using the multimeter's electrical barrier. We know that only the positive electrode of the electrolytic capacitor is connected to the power supply (the black test pen when the power is blocked), and the negative terminal power supply is negative (the red test pen when the power is blocked), the leakage current of the electrolytic capacitor is small (the leakage resistance is large). On the contrary, the leakage current of the electrolytic capacitor increases (the leakage resistance decreases).
When measuring, first assume that a very "+" pole is connected to the black test lead of the multimeter, and the other electrode is connected with the red test lead of the multimeter, and the scale of the stop of the lower needle is stopped (the needle has a large left resistance value), and then The capacitor is discharged (the two leads are touched), the two test leads are reversed, and the measurement is repeated. In the two measurements, the last position of the hand is left (the resistance is large), and the black pen is connected to the positive electrode of the electrolytic capacitor. It is best to use R*100 or R*1K gears for measurement. Use a multimeter to judge the quality of the capacitor.
Use a multimeter to judge the quality of the capacitor
Depending on the capacity of the electrolytic capacitor, the multimeter's R×10, R×100, and R×1K blocks are usually used for testing and judgment. The red and black test leads are respectively connected to the negative pole of the capacitor (the capacitor needs to be discharged before each test), and the yaw of the hands is used to judge the quality of the capacitor. If the hands swing quickly to the right and then slowly return to the left, the capacitor is generally good. If the hands do not turn after swinging, the capacitor has broken down. If the hands are gradually returned to a certain position after the pen is swung, the capacitor has leaked. If the hands are not able to swing, the capacitor electrolyte has dried up and lost capacity.
SMC Board To Board Connector Section.
Compact high density design
Design of super reliable double beam contact
High speed signal transmission rate up to 3 Gbit / S
Polarization to ensure accurate connection
Locating pin for PCB placement
Welded bracket for secure PCB
Wide operating temperature range
Height range of non matching stack
For full automation board components
SMC Board To Board Connector Section
ShenZhen Antenk Electronics Co,Ltd , https://www.pcbsocket.com