1. What is capacitor?
A capacitor is a passive two-terminal electrical component used to store energy electrostatically in an electric field.
2. Type of capacitor?
Fixed Capacitors technologies
Basically all capacitors consist of two electrodes with some kind of dielectric in
between. But there are different technologies to produce the electrodes and the
dielectric, where each one has its special advantages and disadvantages.
Therefore different applications require different types of capacitors.
2.1Vacuum Capacitors
This is the most basic form of capacitor. They consist only of two copper
electrodes within a vacuum. The dielectric constant is therefore 1, so that
vacuum capacitors will only be available for low capacitances.
The technology for vacuum capacitors is similar as for vacuum tubes. Therefore
these capacitors are very expensive.
Advantages:
- Highest dielectric strength of all (high voltage)
- Minimum losses
Disadvantages:
- Low capacitance values only (<1nF)
- Large
- Very expensive
Application:
For high frequency applications within transmitters, where very high voltages
occur and very low losses are required.
2.2. Foil Capacitors:
The electrodes of these capacitors are aluminium foils, the dielectric is oil paper
of different types of plastic foils. The package of electrode-dielectric-electrodedielectric
will be coiled up until the required capacitance is reached.
This type of capacitor provides reasonable electrical properties at reasonable
volume and price. The electrical characteristics will depend on the type of
dielectric used.
Advantages:
- Low series losses due to solid aluminium foil electrodes
- With suitable dielectrics available for high voltages
Disadvantages:
- relatively low capacitance/volume
- no self healing
- considerable inductive component due to coiled electrodes
Application:
HF applications e.g. in tuned circuits where low losses are required.
2.3.
Ceramic Capacitors :
Ceramic capacitors use ceramic materials as dielectric. The electrodes are
produced as a conductive metal film on the ceramic.
We have to distinguish two different types of ceramic dielectric:
Ceramic capacitors with low dielectric constant LDC:
This is the "old" type of ceramic capacitors. The ceramics have dielectric
constants of 10 to 100. The ceramic material must have a certain minimum
thickness, else it breaks easily. Therefore these capacitors are produced with low
capacitance for higher voltages. They have very low losses, especially at high
frequencies.
Advantage:
- low losses at high frequencies
- high dielectric strength (high voltage)
Disadvantage:
- relatively low capacitance/volume (large)
Application:
- r.f. resonant circuits
- high voltages (transmitters)
2.1.1 Variable Capacitors
Mechanically variable capacitors are used to tune resonant circuits and filters in
receivers, transmitters and signal generators.
They are available in the range from 10pF to approximately 500pF.
The capacitance is normally changed by varying the effective area of the
capacitor's electrodes, for some times the electrodes' distances are varied.
Variable capacitors are available with a linear relationship between rotation angle
and capacitance or with a square relationship, as it is required for tuned circuits.
"Butterfly" variable capacitors have two fixed sets of electrodes. The rotating part
couples these electrodes more or less. This has the advantage that the signal
must not be conducted to the rotating part.
Trimmer capacitors:
Trimmer capacitors are used for screw driver adjustment of filters and resonant
circuits. They are mainly ceramic type capacitors, but also air type and plastic foil
type can be found in older equipment. The variation is generally achieved by
changing the relative position of the electrodes to each other. As one electrode is
rotated, the capacitance increases or decreases. Normally the trimmer capacitors
have no dedicated position for maximum and minimum capacitance.
Capacitance Diodes (Varicaps):
Today often capacitance diodes are used for tuning purposes. They allow to
control their capacitance by varying a d.c. voltage. In this way the capacitance
can be changed by the factor 3 to 5. Maximum capacitance of up to 500pF are
available.
The principle of function will be described with the diodes.
Advantages:
- no wear
- simple controls
- possibility for memory and remote control.
Disadvantages
- higher losses than other variable capacitors
- relatively small capacitance values
- non-linear voltage-capacitance relationship
Despite the disadvantages capacitance diodes are today widely used in electronic
equipment, e.g. radio and TV tuners
3.Calculate the value of capacitor?
he first two digits of a ceramic ceramic
capacitor tells us the capacitance in uF and the next digit tells us the negative
power.
Like, if it says 103 then it means it is 10 uF X 10 -3.
Therefore, 0.01uF. Like in the picture the code says 154. So, it means 15 uF X 10-4 = 0.0015 uF
Like, if it says 103 then it means it is 10 uF X 10 -3.
Therefore, 0.01uF. Like in the picture the code says 154. So, it means 15 uF X 10-4 = 0.0015 uF
4. Capacitor test and identify?
Method 1.
Traditional Method to test & check a capacitor
Method 2.
Check & Test a Capacitor By Analog Multimeter ( AVO =
Ampere, voltage, Ohm Meter )
Method 3
Checking Capacitor By Multimeter in the
capacitance Mode
5. Application of capacitor?
Capacitor is a basic storage device to store electrical charges and release it as it is required by the circuit. Capacitors are widely used in electronic circuits to perform variety of tasks, such as smoothing, filtering, bypassing etc….
One type of capacitor may not be suitable for all applications. Ceramic capacitors are generally superior than other types and therefore can be used in a vast ranges of application. The following is the typical capacitor applications in electronic industries:
DC blocking capacitor: In this application the capacitor blocks the passage of DC current (after completely charged) and yet allows the AC to pass at certain portion of a circuit.
Capacitor as a filter: Capacitors are the main elements of filters. There are several types of filters that are used in electronic circuits, such as LPF (Low Pass Filter), HPF(high Pass Filter), BPF (Band Pass Filter), etc…. Since the reactance of the capacitor is inversely related to the frequency, therefore it can be used to increase or decrease the impedance of the circuit at certain frequencies and therefore does the filteration job.
Capacitor as a discharge unit: Capacitors used as a charging unit and the release of the charge (discharge energy) is used for triggering, ignition, and in high scale as a power source.
By Pass capacitor: The reactance of capacitor decreases as the frequency increases. Therefore in certain application it is used in parallel with other components to bypass it at a specified frequency.
Coupling capacitor: The ability of capacitor to pass AC signal, allows it to couple a section of an electronic circuit to another circuit.
Decoupling capacitor: In high speed electronic logic switching causes draw of significant amount of current which in turn would cause disturbance in the logic voltage level. Decoupling capacitor is typically located very close to the IC output and serves as a local energy source to provide the needed extra current and therefore minimizes the noise and disturbances to the logic signal.
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