Question

Capacitors and Inductors

Identify some of the different types of capacitors, and their characteristics. Identify some of the different type of inductors, and their characteristics. It would be appropriate to include small pictures.

Answer 1

Solution :

Capacitor

A capacitor is a device that stores electrical energy in an electric field. It is a passive electronic component with two terminals. A capacitor is made up of two metallic plates. With a dielectric material in between the plates. When you apply a voltage over the two plates, an electric field is created. Positive charge will collect on one plate and negative charge on the other. The figure below shows a capacitor with dielectric.

  

The comparisons between the the different types of capacitor is generally made with regards to the dielectric used between the plates. Some the The different type of capacitor and their characteristics is shown below :

1. Electrolytic capacitor: This capacitor which has two terminals anode and cathode are made of different material. The thin metal film layer is used for one electrode (anode) and for the second electrode (cathode) a semi-liquid electrolyte solution which is in jelly or paste is used. It is generally available in cylindrical package as shown below :

Characteristics :

• The majority of electrolytic types of capacitors are Polarized. (+ve and -ve terminal should be handled carefully)
• Electrolytic capacitors generally have relatively low voltage rating .
• Electrolytic Capacitors have very large capacitance value and capable of storing more charges.
• The applications of this electrolytic capacitors are coupling and decoupling action in circuits.

2. Ceramic Capacitors : The ceramic capacitors are the capacitors and use the ceramic material as a dielectric. It is shown below in the figure

  

. Characteristics :

• Ceramic capacitors have a high dielectric constant (High-K) and are available so that relatively high capacitance’s can be obtained in a small physical size.
• Their capacitance are sensitive to temperature variation in non linear way.
• Ceramic capacitors have values ranging from a few picofarads to one or two microfarads.
• Their voltage ratings are generally quite low.

3. Film Capacitor: The film capacitors are also a capacitor type and they use a thin plastic as the dielectric. There are different types of film capacitors are available like polyester film, metallized film, polypropylene film, PTE film and polystyrene film. It looks like as shown below :

  

Characteristics :

• The some of the film capacitance is a heat resistance and it is used in the aerospace and military technology.
• Some of the thin film capacitor are stable and has very high reliability.

Inductors

An inductor is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a coil around a core. Inductors slow down current surges or spikes by temporarily storing energy in an electro-magnetic field and then releasing it back into the circuit.

.Again Depending on their material type there are several types of inductors which are defined below with their charateristics:

1. Air Core Inductor:  Ceramic is the most commonly used material for inductor cores. Ceramic core inductors are referred as “Air core inductors”. Ceramic has very low thermal co-efficient of expansion, so even for a range of operating temperatures the stability of the inductor’s inductance is high.

  

Characteristics:

• The air core inductors have larger coils to produce higher flux densities.
• These inductors offer high reluctance path for the magnetic flux, hence less inductance.
• There is no loss within the core as air is lossless, and this results in a high level of Q, assuming the inductor or coil resistance is low

2. Iron Core Inductor: These inductor have a core made of solid or laminated iron.

Characteristics:

• Iron cores are normally used for high power and high inductance types of inductor
• These are high power inductors but limited in higher frequency capacity due to the hysteresis and eddy current losses.

3. Bobbin Based Inductor: In this type, coil is wounded on the bobbin. This is shown in the figure below :

Characteristics:

• Bobbin wound inductor designs vary widely in terms of power rating, voltage and current levels, operating frequency, size, impedance, bandwidth (frequency response), packaging, winding capacitance, and other parameters.
• It is mostly designed for : SMPS , Filter circuits or Any application that the inductor can be designed on a bobbin or coil form.