Capacitors are electrical components that stores electricity in form of static charges. Mostly all circuit boards you see consists of capacitors because their functions is beyond storing charges. They are use for regulating current, filtering residual hums from rectified AC to DC, tunning and tank circuits.
Memory cards contains capacitors, a single capacitor and a transistor forms bit of storage, the capacitor acts stores information in form of charges while transistor act as a on and off switch.
There are many types of capacitors varying in sizes, shapes and the applications. But basically there are two major types of capacitors namely;
- Polarised
- Non-polarised.
Polarised capacitor.
Capacitors with polarized terminals are known as polarised capacitors, i.e they are made of positive and negative terminals for connecting to external circuits and are only used in DC. Their negative terminals is connected to negative polarity DC power and it positive terminal connected to positive terminal of a DC power inorder to work properly. Mis-connection in circuits can leads to breakage and swelling of the capacitor plates especially when connected to a high voltage.
Types of polarised capacitors.
1.Electrolytic capacitors. They are the most common types, they have high tolerance and are available at a working voltage of 500v, but their highest capacitance are not available at high voltage. Also they are only used for direct current. Their are two types;
a.Tantalum capacitors.
They are much durable than aluminum capacitors, their dielectric properties is more superior to those of aluminium and therefore they have higher capacitance which makes them suitable for filtering, decoupling and obstructing applications.
b. Aluminum capacitor.
It metal plates are made of aluminium foil, it's the most common type of electrolytic capacitors. The marked line usually white or other color on the main body color indicates the negative polarity and the other pole is the positive pole. Aluminum capacitors are mostly use in AC rectification and RF circuits.
2. Super capacitors.
Just like batteries super capacitors or ultra capacitors stores large amount of electricity in form of static charges. They are made of big metal plates filed with porous powdered carbon which helps to store considerable large amount of charge and seperated by mica or ceramics. Super capacitors are use for regenerative braking systems in electric cars, ultra capacitors gets fully charged in minutes and release current quickly, unlike batteries which takes long time to get fully charged.
non-polarised capacitors.
Non-polarised capacitors don't have polarised terminals. Their leads can be used interchangeably in AC and DC circuits. They are use in high voltage circuits because of their high working voltage as opposed to polarised capacitors but have low capacitance.
Types of non-polarised capacitors.
1. Ceramic capacitors.
They are inexpensive to manufacture. They are made by coating two sides of a small porcelain or ceramic disc with silver and then stacked together to make a capacitor. Ceramic capacitors are available with high and low capacitance depending on the size of the ceramic and it thickness. They are use in high voltage circuit like a thousand volts and also in radio and audio systems.
2.Mica capacitors.
They are known as plastic capacitors because they are made of polystyrene, polycarbonate or Teflon as their dielectric material, thus they have big size and lower capacitance. They are use in AC circuit because they are not polarised. Mica capacitors are mostly used in high radio frequency generation and reception. Their working voltage range from a few volts to 1400v and their plates are usually made from aluminium or zinc.
3. vairable capacitors.
Their capacitance can be varied mechanically, they are mostly find their use in tuning circuits and for matching frequency in LC circuits and for adjusting radio impedance matching in antenna tuner devices.
4. Polyestyrine box capacitors.
Also known as box capacitors, they are available in nano farad and pico farad. They are mostly used in induction heater circuits Box type power capacitors can works on an alternating current voltage ranging from 440v to 700v.
Circuit Applications of capacitors.
1. Removal of ripples from rectified DC from AC.
When AC is rectified (converted) to DC by means of diodes, the output current will contain ripples or unsteady DC, to obtain a steady level of direct current, aluminium capacitors are connected in parallel to the output as shown below.
The capacitor removes ripple when current flows to the capacitor, it quickly gets charge before allowing current to flow across it, thus producing a full rectification.
2. Tank circuit.
capacitors when connected in parallel with an inductor forms an LC or tank circuit. A tank circuit is use for generating oscillatary magnetic field and high frequency, it's usually coupled with coils to produce intermittent RF an example is induction heater, wireless chargers and Tesla coil.
Tank circuit works when direct current flows through a capacitor, and it gets fully charged, current then flows through the inductor and it is stored in form of magnetic field. The magnetic field created then charges back the capacitor. In this way the capacitor is discharged and charged by the inductor with high speed depending on the capacitance of the capacitor and inductance of the inductor.
3. Reduction of sparks
In spark gaps, cars ignition systems and induction coils, capacitors are use for reducing sparks which usually results from shorting of negative and positive terminals of a power source(mostly DC).
In the circuit above current flows from the battery through a switch to an induction coil(for stepping up DC). When the switch is put on sparks occurs at the switch contact due to back EMF, a ceramic capacitor is placed in parallel across it to reduce the spark.
4. Radio tunning circuit.
A variable capacitors is connected in parallel to an inductor forming an LC circuit. The variable capacitor is use to match radio frequency.
In radio circuits the LC circuit is use to tune to different channels of different frequencies, if the frequency of the capacitor is varied to match a specific radio frequency, signals are picked up, which are then amplified and converted to sound.
5.Current and voltage regulation.
Capacitors are use for regulating fluctuating or unstable current and not well connected power source. When connected to an unstable DC source they first get fully charged before allowing any current to flow through them. When fully charged current flows from the capacitor itself as regulated. For example a capacitor connected to a DC source fluctuating unevenly between 12v to 16v, the capacitor gets charged at 16v then it flows from it evenly because it plates are totally occupied with a stable amount of charge.
Capacitors are used along with regulators to stabilise both the input and output voltage as shown above. IC 7805 is a 5V regulator, it is used to regulate 5v from 7.5v. The 100nF regulates the input voltage and the 100nF at the output point regulates the 5v.
6. Filtering of audio signals.
Capacitors are use for filltering audio signals. Audio signals atr flunctuating current or AC, hums and noise are usually arised from direct current.
7. Decoupling.
Capacitors are use for decoupling in circuits but mostly integrated circuits that can't be powered on with flunctuating signals or current
A high capacitance capacitor is usually connected in parallel to the power input before feeding into circuits.
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Basic Electronics