1. The basic concept of a capacitor
a. Capacitance: The amount of electricity required to raise a unit potential per conductor.
C=q/U (coulomb/volt)
b. Units (Fara F)
1F=1 Coulomb/1 Volt=106μF=1012pF
1μF=103nF
c. Capacitors: Containers that contain a plurality of electrical conductors that can store electrical charges.
CAB=QA/(UA- UB)
d. Connection of capacitors:
Series: 1/Cs=1/C1+1/C2
Parallel connection: Cp=C1+C2
2. The basic parameters of the capacitor
2.1 Capacitance C C = (t × f);
2.2 loss tangent D D = tg δ = P is / P that is the total power through the capacitor and the heat dissipation in the capacitor D = D (f × t);
2.3 Withstand voltage Vt-t: The dielectric strength through the dielectric field is related to the electrical stress, V = V (f × t)
2.4 Insulation resistance RI (leakage current): intrinsic leakage current and absorption current inside the medium;
2.5 Overcurrent capability (dv/dt) Ip=C dv/dt;
2.6 Temperature T : The highest/lowest operating temperature of the capacitor (-40/105);
2.7 Thermal stability (Δt-t): time required for the temperature rise to reach stability when the capacitor is normally heated (2h, 48h);
2.8 Self-healing (SH): Self-recovery after dielectric breakdown (ΔC/C ≤ 0.5%, self-healing times <2 times);
2.9 Security
(1).Flame retardant (UL94V-0)
(2). Explosion-proof P0 P1 P2 three levels;
2.10 Durability (Life Grade) Conditions: Voltage 1.25Un/1.4Un Temperature T=Tmax Continuous Operation
A level 160000h
Class B 100000h
Class C 50000h
D level 10000h
2.11 The reliability grade (λ: failure rate 10-λ) is divided into five grades, six grades, seven grades, and eight grades.
3. Classification and characteristics of capacitors:
3.1 Classified by Media
(1) Metallized paper dielectric capacitors, the representative models are: CJ10, CJ41, CJ48, CJ3, CJD, CJZ, CJMJ and so on. Paper capacitors, the representative models are: CZ, CZM, CZK, CZC, CZY and so on. This type of capacitor has a higher specific capacitance and a smaller volume, but it has a larger loss and a lower insulation resistance. It is mainly used in DC or low-frequency circuits where the AC component is less than the rated DC voltage and it is admissible to occasionally have low insulation resistance and transient breakdown. The applied AC peak value shall not exceed 20% of the rated DC voltage; the sum of the DC voltage and AC voltage shall not exceed the rated DC voltage value.
(2) Organic film capacitors, representative models for high frequency range are: polystyrene CB, CBM, CBF, CBJ-L, CBMJ and polypropylene CBB, CBBS. This type of capacitor is characterized by small dielectric loss, high insulation resistance, low absorption coefficient, good temperature stability, and stable frequency characteristics. It is applicable to low-voltage and energy-storage polyester capacitor CL and carbon film capacitor CQ. It has good heat resistance, high compressive strength, large specific capacitance, and high temperature performance. The CBMJ is suitable for standard capacitors with an accuracy of up to ±0.05%. This capacitor can be used in a wide temperature range, requiring high insulation resistance, low dielectric absorption, or low loss circuits. The sum of the AC voltage and DC voltage of the applied voltage must not exceed the rated DC voltage value. Do not exceed 20% (at 60HZ), 15% (120HZ), or 1% (1000HZ) of the rated DC voltage.
(3) Ceramic capacitors, the representative models are: Type 1 ceramic capacitors (CC, CCG, CCW, CCWY, CCSD, CCTD, CCM, etc.) are mainly used for high stability circuits and temperature compensation circuits. Their loss tangent is low, and the medium system has a small range of changes. Among them, the monolithic ceramic capacitor (CC4D) has the characteristics of high specific capacitance, low dielectric loss, high insulation resistance and stable capacity. They can work effectively in high-value, ultra-high-value or microwave sections. They are especially suitable for resonant circuits or other circuits that require low loss and stable capacity. Type 2 ceramic capacitors have a high dielectric coefficient and a large loss. The tangent value, its capacity and the tangent of the loss tangent are all poor in frequency-temperature characteristics. Mainly used in small, large-capacity circuits. These capacitors can be used as bypass, filter, and non-magnetic coupling elements for high frequency circuits that allow capacitance to change with temperature. Typical applications are audio and RF resistive-capacitive coupling, radio frequency, and intermediate frequency emitter bypass. It can be used for the loss factor is not critical, even if due to temperature, voltage and frequency changes caused by moderate changes, will not affect the normal function of the circuit circuit.
(4) Mica capacitors, the representative models are: CY, CYRX, CYS, CYM, etc. It is characterized by small dielectric loss, high electrical strength, stable frequency and temperature characteristics, and high capacitance accuracy. Can be used in circuits with high precision requirements, or in high frequency filtering and bypassing, coupling circuits; can be used on circuits with very strict impedance tolerances related to temperature, frequency, aging, etc.; can be used as a tuned circuit pad The entire capacitor, secondary capacitor standard use. Mica capacitors operate at frequencies up to 500 MHz and can be used in VHF coupling, bypass, and tuning circuits.
In general, the operating voltage of the capacitor is reduced when the operating temperature and operating frequency are increased. Capacitors can be highly reliable if they are properly protected against high temperatures and moisture. Otherwise, due to the long-term effects of high temperature, high humidity, and DC voltage stress, the capacitor is exacerbated by the silver ion migration process on the silver mica sheet, which will result in a decrease in capacitance, insulation resistance, and operating electric field strength.
The failure of a component depends on its application conditions. At room temperature, the life of the capacitor is inversely proportional to the 8th power of the direct source operating voltage; under a constant DC voltage condition, the life of the capacitor is reduced by approximately 50% for every 10 degrees of temperature increase.
(5) Glass capacitors. Its representative models are: CI, CII, etc. Such capacitors are used in circuits that need to consider different temperature coefficients and dielectric losses, and can replace mica capacitors. It is stable and has a long life under harsh working environment conditions. Can withstand high acceleration stress. However, it is vulnerable to moderate mechanical damage. Therefore, be careful. They are more tolerant to high velocity stresses than mica capacitors and have a wide range of capacitance.
Under the long-term effects of high temperature, high humidity, and DC voltage stress, silver ion migration may occur, resulting in a decrease in operating voltage and even the risk of an electrode short circuit.
(6) Aluminum electrolytic capacitors, whose representative models are CD, CDZ, CDA, CDM, CDW, CDS, CDJ, CDDS, CDXW, CDL-T, CDX, etc. The advantages are small size, large capacity, and low price. The station is used for filtering, coupling and bypass circuits. In these cases, only a large capacity value is required, and the allowable capacity can greatly exceed the standard value of the capacitor.
For polar capacitors, the sum of the applied ac peak and dc voltage must not exceed the rated dc working voltage of the capacitor.
For aluminum electrolytic capacitors that are not used for a long period of time, since the aluminum oxide film may be eroded, the leakage current becomes large, and the rated DC operating voltage is instantaneously added, a large amount of gas is generated inside the capacitor, so that the housing is opened top. Therefore, capacitors that are not used for a long period of time should be gradually increased in voltage and used to be sophisticated. High-voltage capacitors should be especially noted. Normally, the aluminum electrolysis containers that have been in stock for more than two years will not be installed.
(7) Due to body yttrium and tantalum electrolytic capacitors, the representative models are: CCTF, CCTJ, CCDD, CCM, CCX, CA9, CA41, CA43, CA70, CAP, CAK, CA, CN (铌), etc. Among the existing electrolytic capacitors, the ones with the most stable performance, the most reliable, the longest life, and the best storage performance. Not sensitive to temperature. The disadvantage is that the leakage current is large and the voltage range is small (6-120) volts. The maximum allowable reverse current is 1% at a positive DC voltage of 25 degrees.
This type of capacitor can be used in circuits that need to bypass or filter low-frequency or pulsating current components, as well as in coupling and feedback circuits; it requires high-capacity, small-volume, high-impact shock and vibration stress. .
Can be used for filtering, bypassing, coupling, DC blocking, energy storage, and other low-voltage DC circuits. When a polar capacitor is in use, it is necessary to pay attention to the polarity of the DC voltage. At the same time, the maximum allowable reverse voltage is not more than 1 volt.
Non-polar sintered tantalum solid capacitors can be used in calibration networks of automatic control systems with operating voltages of 6.3-63 volts as integration, filtering, and coupling capacitors; or in circuits where the polarity of a DC voltage reverses, such as tuned circuits, low frequencies Circuits, AC motor circuits, and computer circuits.
(8) Liquid tantalum electrolytic capacitors, their representative models are: CAI, CA30, CA51S, CA34A, CA341, CA342, etc. This type of capacitor is a polar capacitor, which has the largest specific capacitance and small leakage current, and is mainly used for large electricity. Capacity, while allowing large capacity deviation circuits, is used as a bypass or filter for low-frequency ripple DC components. When used for low-frequency coupling of tube and transistor circuits, leakage currents must be allowed. Liquid tantalum electrolytic capacitors do not have the ability to withstand reverse voltage, so they are only used in DC circuits and should pay special attention to polarity. Its poor sealing, work under low pressure, prone to liquid leakage phenomenon, causing performance changes, leading to failure. The electrolytic solution inside this capacitor is acidic and has a corrosive effect on the housing. Severe leakage can cause failure. For AC components, the sum of the peak AC voltage and the applied DC voltage must not exceed the rated DC voltage. At the same time the peak AC voltage must not exceed the applied DC voltage.
(9) Feedthrough capacitors for RF anti-interference filters. Low-frequency current or RF current (which may cause interference) flowing through a housing or device at some point is grounded through the shortest possible path.
Typical applications are: rotary devices; ignition devices; electromechanical regulators, vibrators, switches; electronic devices (transmitters, radar modulators, thyristors, etc.) and equipment AC filters.
(10) Ceramic trimmer capacitors are used on circuits that need to be carefully adjusted on a regular basis. They are often used in RF, IF, oscillation, phase adjustment, and frequency discrimination. The capacitance and its adjustment component are linear, and the change of capacitance with temperature is non-linear. Within the capacity range, the sensitivity to temperature is also non-linear. This capacitor cannot be used for temperature compensation. This small trimmer capacitor is quite stable in shock and vibration environments. If a higher stable width is required, an air trimmer capacitor should be used.
(11) Air trimmer capacitors are used in the same way as "ceramic trimmer capacitors", but this is a more stable temperature stability of the container.
3.2 According to the shape classification: split, winding and so on.
4. Capacitor certification system
4.1 UL certification
4.2VDE certification
4.3CQC certification