Classic Capacitor Knowledge

Classic capacitor knowledge

1.Capacitor :

The so-called capacitor is an electronic component that holds and releases electric charge. The basic working principle of a capacitor is to charge and discharge, pass AC, and block DC. Of course there are rectification, oscillation and other functions. In addition, the structure of the capacitor is very simple, mainly composed of two positive and negative electrodes and an insulating medium sandwiched in between, so the capacitor type is mainly determined by the electrodes and the insulating medium.

Capacitors have many uses, the main ones are as follows:

a.DC blocking: The function is to prevent DC from passing through and allow AC to pass through.

b.Bypass (decoupling): Provides a low-impedance path for certain parallel components in an AC circuit.

c.Coupling: serves as a connection between two circuits that allows AC signals to pass through and be transmitted to the next circuit

d.Filtering: This is very important for DIY. The capacitors on the graphics card basically have this function.

e.Temperature compensation: Compensate for the impact of other components’ insufficient adaptability to temperature to improve the stability of the circuit. 6． Timing: Capacitors are used in conjunction with resistors to determine the time constant of a circuit.

f.Tuning: System tuning of frequency-dependent circuits, such as cell phones, radios, and televisions.

g.Rectification: Opening or closing a semi-closed conductor switch assembly at a predetermined time.

h.Energy storage: Stores electrical energy and releases it when necessary. Such as camera flash, heating equipment, etc.

2.Unit of capacitance :

The basic unit of capacitance is: F (farad). In addition, there are μF (microfarad) and pF (picofarad). There is also a less used unit, which is: nF (). Since the capacity of the capacitor F is very Large, so what we see are generally units of μF, nF, and pF, not F units.

The specific conversion between them is as follows:
1F=1000000μF
1μF=1000nF=1000000pF

3.Calculation method of capacitance:

a.Capacitance calculation formula

The amount of electricity Q that can be charged into a capacitor is not infinite. As the potential difference changes, the electricity Q also increases. For the same capacitor, it is a constant that has nothing to do with the amount of electricity and potential difference. For different capacitors, the potential difference increases. The amount of electricity required to increase 1 volt is different, that is, it is a different constant. Therefore, we think it can reflect the ability of the capacitor to accommodate charge, and thus defines a new physics – capacitance, symbol C , let C=

①Definition: Capacitance is a physical quantity that describes the characteristics of the capacitor’s ability to hold electricity. Its size can be measured by the ratio of the band area of one pole of the capacitor to the potential difference between the two plates.

②Measurement: C=

b.Calculation of capacitor impedance

Alternating current can pass through capacitors, but capacitors still hinder alternating current. The blocking effect of capacitor on alternating current is called capacitive reactance. The capacitance is large, and the alternating current can easily pass through the capacitor, which means that the capacitance is large, and the hindering effect of the capacitor is small; the frequency of the alternating current is high, and the alternating current can easily pass through the capacitor, which means that the frequency is high, and the obstructing effect of the capacitor is also small. Experiments have shown that capacitive reactance is inversely proportional to capacitance and frequency. If the capacitive reactance is represented by XC, the capacitance is represented by C, and the frequency is represented by f _,    We know the frequency f and capacitance C of the alternating current.

4.Capacitor model naming:

1) The model naming of capacitors in various countries is very inconsistent. The naming of domestic capacitors consists of four parts:
Part 1: Use letters to indicate the name, and the capacitor is C.
Part 2: Use letters to represent materials.
Part 3: Representing categories with numbers.
Part 4: Use numbers to represent serial numbers.

2) Marking methods of capacitors:
(1) Direct marking method: Use letters and numbers to mark the model and specifications directly on the casing.
(2) Text symbol method: Use a regular combination of numbers and text symbols to express capacity. Text symbols represent the units of capacitance: P, N, u, m, F, etc. It is expressed in the same way as resistance. The nominal allowable deviation is also expressed in the same way as the resistance. For capacitances less than 10pF, the allowable deviations are replaced by letters: B——±0.1pF, C——±0.25pF, D——±0.5pF, F——±1pF.
(3) Color marking method: It is the same as the expression method of resistance, and the unit is generally pF. The withstand voltage of small electrolytic capacitors is also color-coded. The position is close to the root of the positive lead wire. The meaning is as shown in the following table:
Color: black brown red orange yellow green blue purple gray
withstand voltage: 4V 6.3V 10V 16V 25V 32V 40V 50V 63V

3) Safety capacitors are used in situations where the failure of the capacitor will not cause electric shock or endanger personal safety.

Safety capacitor safety level, allowable peak pulse voltage in application, overvoltage level (IEC664)

X1 >2.5KV ≤4.0KV Ⅲ

X2 ≤2.5KV Ⅱ

X3 ≤1.2KV —

Safety capacitor grade system insulation type rated voltage range

Y1 double insulation or reinforced insulation ≥250V

Y2 basic insulation or supplementary insulation≥150≤250V

Y3 basic insulation or supplementary insulation≥150≤250V

Y4 basic insulation or supplementary insulation <250V

The capacitance of the Y capacitor must be limited to achieve the purpose of controlling the leakage current flowing through it under the action of rated frequency and rated voltage and its impact on the EMC performance of the system. GJB151 stipulates that the capacity of the Y capacitor should not be greater than 0.1FY In addition to complying with the corresponding grid voltage withstand voltage, the capacitor is also required to have adequate safety capacitor parameter selection in terms of electrical and mechanical properties.
(4) Marking method of imported capacitors: Imported capacitors generally consist of 6 items.
The first item: Use letters to indicate the category:
The second item: Use two digits to indicate its shape, structure, packaging method, lead start and relationship with the axis.
Item 3: Temperature characteristics of temperature compensation capacitors. There are letters and colors. The meanings are as shown in the following table:
Serial number letter color temperature coefficient allowable deviation letter color temperature coefficient allowable deviation
1 A Gold +100 R Yellow -220
2 B Gray+30 S Green-330
3 C Black 0 T Blue-470
4 G ±30 U Purple-750
5 H Brown-30 ±60 V -1000
6 J ±120 W -1500
7 K ±250 X -2200
8 L Red -80 ±500 Y -3300
9 M ±1000 Z -4700
10 N ±2500 SL +350~-1000
11 P Orange -150 YN -800~-5800
Note: The unit of temperature coefficient is 10e -6/℃; allowed The deviation is %.
Item 4: Use numbers and letters to represent the withstand voltage. The letters represent valid values and the numbers represent the power of 10 of the multiplicand.
The fifth item: nominal capacity, expressed by three digits, the first two are valid values, and the third is the power of 10. When there are decimals, use R or P. The unit of ordinary capacitor is pF, and the unit of electrolytic capacitor is uF.
Item 6: Allowable deviation. Represented by one letter, the meaning is the same as that of domestic capacitors.
There is also a color marking method, which has the same meaning as the marking method of domestic capacitors.
3. The main characteristic parameters of the capacitor:
(1) Capacity and error: the maximum allowable deviation range between the actual capacitance and the nominal capacitance. Generally divided into three levels: Level I ±5%, Level II ±10%, and Level III ±20%. In some cases, there is also level 0, with an error of ±20%.
The allowable error of precision capacitors is smaller, while the error of electrolytic capacitors is larger, and they adopt different error levels.

The precision level of commonly used capacitors is the same as that of resistors. Represented by letters:

(2) Rated working voltage: The maximum DC voltage that a capacitor can withstand in a circuit that can work stably and reliably for a long time is also called withstand voltage. For devices with the same structure, medium, and capacity, the higher the withstand voltage, the larger the volume.
(3) Temperature coefficient: within a certain temperature range, the relative change in capacitance for every 1°C change in temperature. The smaller the temperature coefficient, the better.
(4) Insulation resistance: used to indicate the size of leakage. Generally, the insulation resistance of small-capacity capacitors is very large, ranging from hundreds of megaohms to several thousand megaohms. The insulation resistance of electrolytic capacitors is generally small. Relatively speaking, the larger the insulation resistance, the better, and the leakage will be smaller.
(5) Loss: Under the action of the electric field, the energy consumed by the capacitor to generate heat per unit time. These losses mainly come from dielectric loss and metal loss. Usually expressed by the loss tangent value.
(6) Frequency characteristics: The electrical parameters of the capacitor change with the frequency of the electric field. For capacitors operating at high frequencies, since the dielectric constant is smaller at high frequencies than at low frequencies, the capacitance is also reduced accordingly. Losses also increase with frequency. In addition, when operating at high frequency, the distribution parameters of the capacitor, such as the resistance of the pole piece, the resistance between the lead and the pole piece, the self-inductance of the pole piece, the lead inductance, etc., will affect the performance of the capacitor. All of this limits the frequency of use of capacitors.
Different types of capacitors have different maximum usage frequencies. Small mica capacitors are within 250MHZ; disc type porcelain capacitors are 300MHZ; round tube type porcelain capacitors are 200MHZ; disc type porcelain capacitors can reach 3000MHZ; small paper dielectric capacitors are 80MHZ; medium paper dielectric capacitors are only 8MHZ.

5.Types of capacitors:

Due to different insulating materials, the types of capacitors are also different:
according to the structure, they can be divided into: fixed capacitors, variable capacitors, and trimmer capacitors.
According to the dielectric material, it can be divided into: gas dielectric capacitor, liquid dielectric capacitor, inorganic solid dielectric capacitor, organic solid dielectric capacitor and electrolytic capacitor.
According to polarity, they are divided into: polarized capacitors and non-polar capacitors. The most common one we see is electrolytic capacitors.

In principle, they are divided into: non-polar variable capacitors, non-polar fixed capacitors, polar capacitors, etc.

In terms of materials, they can be divided into: CBB capacitors (polyethylene), polyester capacitors, ceramic capacitors, mica capacitors, monolithic capacitors, electrolytic capacitors, tantalum capacitors, etc. The following are the advantages and disadvantages of various capacitors:

Non-inductive CBB capacitors are made of
2 layers of polypropylene plastic and 2 layers of metal foil alternately mixed and then bundled. Non-inductive, good high-frequency characteristics, small size
and not suitable for large capacity, relatively high price, and poor heat resistance.
CBB capacitors
are made of two layers of polyethylene plastic and two layers of metal foil alternately mixed and then bundled. Yes, the rest is the same as above.

Ceramic capacitors

It is a capacitor that uses ceramic material as the dielectric, coats the ceramic surface with a metal film, and then sinters it at high temperature as an electrode . According to material and working voltage, they can be divided into: low-voltage ceramic capacitors and high-voltage ceramic capacitors. Its characteristics are: small size, good heat resistance, low loss, high insulation resistance, but small capacity. Suitable for use in high-stable oscillation circuits as loop, bypass capacitors and pad capacitors.

Mica capacitor

Capacitors that use natural mica as the medium in the middle of the capacitor are made by using metal foil or spraying a silver layer on mica sheets as electrode plates. After the electrode plates and mica are laminated layer by layer, they are then die-cast in bakelite powder or sealed in a ring. Made of oxygen resin. Because mica has excellent properties such as high dielectric strength, large dielectric constant, low loss, high chemical stability, good heat resistance, and is easy to peel into thin sheets with uniform thickness, mica capacitors are widely used in the stability and stability of capacitance. In circuit situations with high reliability requirements.

Monolithic capacitor

Small size, large capacity; low loss, small error; low temperature, high precision.

No polarity, no cross-interference, tape (roll) packaging suitable for automated, high-density installation.

Epoxy resin encapsulation has excellent moisture resistance, mechanical strength resistance and welding heat resistance.

The horizontal axial monolith fills the performance shortcomings of chip capacitors and achieves miniaturization and integration of product circuits.

electrolytic capacitor

Two pieces of aluminum strips and two layers of insulating films are stacked on top of each other, turned into bundles and soaked in an electrolyte (synthetic solution containing acid).

large capacity.
High frequency characteristics are not good.

The role of electrolytic capacitors in the circuit:
1. Filtering effect: In the power circuit, the rectifier circuit turns AC into pulsating DC, and a larger-capacity electrolytic capacitor is connected after the rectifier circuit to use its charging and discharging characteristics to make The rectified pulsating DC voltage becomes a relatively stable DC voltage. In practice, in order to prevent the supply voltage of each part of the circuit from changing due to load changes, electrolytic capacitors of tens to hundreds of microfarads are generally connected to the output end of the power supply and the power input end of the load. Since large-capacity electrolytic capacitors generally have a certain inductance and cannot effectively filter out high-frequency and pulse interference signals, a capacitor with a capacity of 0.001–0.lpF is connected in parallel at both ends to filter out high-frequency signals. and pulse interference.

2. Coupling effect: In the process of transmission and amplification of low-frequency signals, in order to prevent the static operating points of the front and rear circuits from affecting each other, capacitive coupling is often used. In order to prevent excessive loss of low-frequency components in the signal, electrolytic capacitors with larger capacities are generally used.

Tantalum capacitor

Metal tantalum is used as the positive electrode, and metal is sprayed outside the electrolyte as the negative electrode.

Good stability, large capacity, and good high-frequency characteristics.
The cost is high. (generally used in key places)

Chip capacitors

1.NPO capacitor (temperature compensated chip monolithic ceramic capacitor)

NPO is one of the most commonly used monolithic ceramic capacitors with temperature compensation characteristics. Its filling medium is composed of rubidium, samarium and some other rare oxides. NPO capacitors are among the most stable in capacitance and dielectric loss. When the temperature is from -55℃ to +125℃, the capacity change is 0±30ppm/℃, and the change in capacitance with frequency is less than ±0.3ΔC. The drift or hysteresis of NPO capacitors is less than ±0.05%, which is negligible compared with film capacitors greater than ±2%. The typical change in capacity relative to service life is less than ±0.1%. NPO capacitors have different capacitance and dielectric loss characteristics with frequency depending on the packaging form. Large package sizes have better frequency characteristics than small package sizes. The following table gives the selectable capacity range of NPO capacitors.

NPO capacitors are suitable for use as tank capacitors in oscillators and resonators, as well as coupling capacitors in high-frequency circuits.

2.X7R capacitor(Temperature stable ceramic capacitor)

X7R capacitors are called temperature-stable ceramic capacitors. When the temperature is from -55°C to +125°C, the capacitance change is 15%. It should be noted that the capacitor capacity change is non-linear at this time.
The capacity of the X7R capacitor is different under different voltage and frequency conditions, and it also changes with time, changing approximately 1%ΔC every 10 years, which means a change of about 5% in 10 years.
X7R capacitors are mainly used in less demanding industrial applications and under conditions where the change in capacitance when the voltage changes is acceptable. Its main feature is that the capacitance can be larger under the same volume. The following table shows the selectable capacity range of X7R capacitors.

3.Z5U capacitor (“universal” ceramic capacitor)

Z5U capacitors are called “universal” ceramic monolithic capacitors. The first thing to consider here is the operating temperature range. The main thing for the Z5U capacitor is its small size and low cost. For the above three types of ceramic monolithic capacitors, the Z5U capacitor has the largest capacitance under the same volume. However, its capacitance is greatly affected by the environment and working conditions, and its aging rate can decrease by up to 5% every 10 years.

Although its capacity is unstable, it has a wide range of applications due to its small size, low equivalent series inductance (ESL) and equivalent series resistance (ESR), and good frequency response. Especially in the application of decoupling circuit. The following table gives the value range of the Z5U capacitor.

Package DC=25V DC=50V

0805 0.01μF—0.12μF 0.01μF—0.1μF

1206 0.01μF—0.33μF 0.01μF—0.27μF

1210 0.01μF—0.68μF 0.01μF—0.47μF

2225 0.01μF—1μF 0.01μF—1μF

Other technical specifications of Z5U capacitors are as follows:

Working temperature range +10℃ — +85℃

Temperature characteristics +22% —- -56%

Maximum dielectric loss 4%

4.Y5V capacitor(General purpose capacitors with certain temperature limits)

Y5V capacitor is a general capacitor with certain temperature limits. Its capacity can change from +22% to -82% in the range of -30℃ to 85℃.

The high dielectric constant of Y5V allows capacitors up to 4.7µF to be fabricated in smaller physical sizes.

The value range of Y5V capacitor is shown in the table below

Package DC=25V DC=50V
0805 0.01μF—0.39μF 0.01μF—0.1μF
1206 0.01μF—1μF 0.01μF—0.33μF
1210 0.1μF—1.5μF 0.01μF—0.47 μF
2225 0.68μF—2.2μF 0.68μF—1.5μF

Other technical specifications of Y5V capacitors are as follows:

Working temperature range -30℃ — +85℃

Temperature characteristics +22% —- -82%

Maximum dielectric loss 5%