PCB technology electrolytic capacitors and capacitors
one. Fixed capacitor: refers to once made, its capacitance can no longer change the capacitor.
Capacitors can generally be divided into non-polar ordinary capacitors and electrolytic capacitors with polarity. Ordinary capacitors are divided into fixed capacitors, semi-adjustable capacitors (trimmer capacitors), variable capacitors.
- Capacitor classification: Capacitors are generally classified by dielectric.
1) Paper dielectric: general capacity of dozens of picofarads (pF) to zero a few micro-method (uF), with a pressure of 250V, 400V, 630V, etc., the capacity error is generally: ± 5%, ± 10%, ± 20 %. Another is a metalized paper dielectric, the most important feature is a limited self-healing ability. Generally can not be used in high frequency circuits, the working frequency is only a few dozen KHZ.
2) Polyester capacitor:
3) Polystyrene capacitor:
4) Polypropylene capacitor:
5) Teflon capacitors:
6) Polyimide film capacitors:
7) Polycarbonate film capacitors:
8) Composite film capacitors:
9) Film capacitors:
10) Laminated Metallized Polycarbonate Capacitor:
11) Mica capacitors:
12) Ceramic capacitors: low price, wide range of applications. Divided into low-voltage low-power and high-pressure high-power 2 kinds.
Low-voltage low-power ceramic capacitors in accordance with the performance of the materials used, can be divided into I and II type. Type I is characterized by low dielectric loss, capacitance, temperature, frequency, voltage and time stability are better, commonly used in high-frequency circuits. Type II is characterized by small size, but poor stability, dielectric loss, commonly used in low-frequency circuits. UHF ceramic capacitors can be used for the frequency of not more than 500MHZ high-frequency circuits.
High voltage high power ceramic capacitors, usually only suitable for low loss, low power circuit.
13) Glass glaze capacitor:
- Capacitor model name:
1) The national capacitor model name is not uniform, the name of the domestic capacitor consists of four parts:
The first part: the name of the alphabet, the capacitor is C.
Part II: Letters indicate the material.
The third part: Numerical classification.
Part IV: Numeric representation of serial numbers.
2) Capacitor logo method:
(1) Straight mark method: Use letters and numbers to model, specifications directly marked on the shell.
(2) text symbol law: with numbers, text symbols, a regular combination of capacity. Text symbols indicate the unit of capacitance: P, N, u, m, F, etc. The same way as resistance. The nominal allowable deviation is also the same as the resistance representation. Capacitance of less than 10pF, the allowable deviation with letters instead: B – ± 0.1pF, C – ± 0.2pF, D – ± 0.5pF, F – ± 1pF.
(3) color standard method: and the resistance of the same way, the unit is generally pF. Small electrolytic capacitor voltage is also useful color scale method, the location close to the root of the cathode lead, the significance of the table below:
Color dark red orange yellow green blue purple gray
Withstand voltage 4V 6.3V 10V 16V 25V 32V 40V 50V 63V
(4) mark the method of imported capacitors: Imported capacitors generally have 6 components.
First item: Alphabetical category:
The second: two figures that its shape, structure, packaging, the beginning of the wire and the relationship with the shaft.
Third: temperature compensated capacitor temperature characteristics, useful letters, but also useful color, the significance of the following table:
No. Letter Color Temperature Coefficient Tolerance Letter Color Temperature Coefficient Tolerance
1 A gold +100 R yellow -220
2 B ash +30 S green -330
3 C Black 0 T Blue -470
4 G ± 30 U Violet -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 of 10e -6 / ℃; allowable deviation is%.
Fourth: pressure and pressure with numbers and letters, letters represent the effective value, the figure represents the multiplicand of the power of 10.
Fifth: The nominal capacity, said with three digits, the first two significant figures, the third is a power of 10. When there are decimals, with R or P said. The unit of common capacitor is pF, and the unit of electrolytic capacitor is uF.
Sixth: allow deviation. In a letter, the meaning and the same capacitor made in China. Also useful color method, the meaning and the same method of marking domestic capacitors.
- The main characteristics of the capacitor parameters:
(1) Capacity and error: The maximum allowable deviation range of actual capacitance and nominal capacitance. Generally divided into three levels: I ± 5%, II ± 10%, III ± 20%. In some cases, there are 0 levels with an error of ± 20%. The allowable error of the precision capacitor is smaller, and the error of the electrolytic capacitor is bigger, they adopt different error grades.
Commonly used capacitors have the same accuracy class as resistors. Letters: D – 005 – ± 0.5%; F – 01 – ± 1%; G – 02 – ± 2%; J – I – ± 5% Class II – ± 10%; Class M – III – ± 20%.
(2) Rated working voltage: Capacitors in the circuit can be long-term stability, reliable work, the maximum withstand DC voltage, also known as pressure. For the structure, medium, the same capacity of the device, the higher the pressure, the greater the volume.
(3) temperature coefficient: Within a certain temperature range, the temperature change of 1 ℃, the relative change in capacitance. The smaller the temperature coefficient, the better.
(4) Insulation resistance: used to indicate the size of the leakage. General small-capacity capacitors, large insulation resistance, in the hundreds of megaohm or several giga-ohms. Electrolytic capacitor insulation resistance is generally small. Relatively speaking, the larger the insulation resistance, the better the leakage.
(5) Loss: Under the action of the electric field, the capacitor consumes energy during the unit time. These losses come mainly from dielectric loss and metal loss. Usually loss tangent value to represent.
(6) frequency characteristics: the electrical properties of capacitors with the electric field frequency and the nature of the change. Capacitors operating under high frequency conditions have lower capacitance due to their lower dielectric constant at high frequencies than at lower frequencies. Losses also increase with increasing frequency. In addition, the distribution of capacitors, such as the pole piece resistance, the resistance between the lead and the pole pieces, the pole piece’s own inductance, the lead inductance, etc., can affect the performance of the capacitor during high frequency operation. All of these make the use of capacitors limited.
Different varieties of capacitors, the highest frequency of use is different. Small mica capacitors within 250MHZ; wafer type ceramic capacitors to 300MHZ; circular tube type ceramic capacitors to 200MHZ; disc type porcelain up to 3000MHZ; small paper dielectric 80MHZ; medium-sized paper capacitors only 8MHZ.
- Circuit symbols:
- The use of capacitors:
1) Choose the right model:
2) Reasonably determine the accuracy of the capacitor:
3) Determine the rated capacitor voltage: For general circuits, the operating voltage of the circuit should be 10% ~ 20% of the rated voltage of the capacitor; when there is ripple voltage, the operating voltage should be the highest voltage pulsating. When applied to AC, the rated voltage increases with increasing frequency. When the temperature and the environment is relatively high, the rated voltage but also use a larger choice.
4) try to choose a large insulation resistance capacitance:
5) Consider the temperature coefficient and frequency characteristics:
6) pay attention to the use of the environment:
two. Electrolytic capacitor:
Electrolytic capacitors generally have positive and negative points, that is, with polarity. Therefore, when used in the circuit is positive and negative can not take the wrong. Electrolytic capacitors that are now non-polar or used for AC circuits are now available, called bipolar or non-polar electrolytic capacitors. Under the action of applied voltage, the device which is damaged locally for some reason has the function of self-repairing. This phenomenon is called self-healing of electrolytic capacitor.
Electrolytic capacitors generally only -20 ℃ ~ +70 ℃ within the scope of use. Features by temperature, frequency of a great influence. Commonly used are generally aluminum electrolytic capacitors. Aluminum electrolytic capacitor model is generally CDXX, capacity, voltage, positive and negative are marked on the shell. Sometimes the length of the lead to that long-term positive, short-term negative.
Aluminum electrolytic capacitor loss, temperature, frequency characteristics of poor, limiting the application of the AC circuit.
three. Tantalum electrolytic capacitor:
Tantalum electrolytic capacitors are used tantalum electrodes for tantalum oxide as a dielectric capacitor. Characteristics are: high chemical stability, high rated pressure, high temperature performance, high mechanical strength, small size. Commonly used CA logo, its capacity from 0.47uF to 1000uF, rated voltage mainly 6.3V, 10V, 16V, 63V several. Performance is much better than aluminum electrolytic capacitors, but the price is more expensive.
Other electrolytic capacitors niobium electrolytic capacitors, better performance, smaller size. Titanium electrolytic capacitors, tantalum – niobium electrolytic capacitors.
four. Micro capacitor:
- Chip ceramic capacitors: surface mount capacitors. Capacity range of 1pF ~ 47800pF, with a voltage of 25V, 50V. Package mounting dimensions and the same surface mount resistance.
- Flake tantalum capacitors: small size, large capacity. Welding temperature limit below 280 ℃, the time is less than 10S. Its capacity range of 0.1uF ~ 100uF, DC voltage is 4 ~ 50V, commonly used voltage is 16V, 35V and so on.
- Semiconductor Capacitor:
- Electrolytic capacitor: Between the battery and capacitor, with large capacity, known as the super capacitor. Generally only for DC or low frequency conditions, often used as energy storage components.