Maximum power transfer theorems

The maximum-power transfer theorem has effective applications in stereo amplifier design, where it is essential to maximize power delivered to speakers, and it is useful in electric vehicle construction, where it is required to maximize power supplied for driving a motor.

A network that consists of linear impedances & 1 or more voltage or current sources can be reduced to a Théven in equivalent circuit.When a load is connected to the terminals of this equivalent circuit, power is transferred from the source to the load.

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Main effects of electric current

There are three main effects of an electric current:

(a) magnetic effect

(b) chemical effect

(c) heating effect

Listed below are few practical applications and uses of these effects of an electric current:

• Magnetic effect:

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Magneto motive force and magnetic field strength

The Magneto-motive force (mmf) is the cause due to the presence of the a magnetic flux in a magnetic circuit,

mmf,Fm=NI amperes

where N is used to represent the number of conductors (or turns) and I represents the current in amperes. We sometimes express the unit of mmf as ‘ampere-turns’. As we know, since ‘turns’ have no dimensions, the SI unit of mmf is the ampere. Magnetic field strength (or magnetizing force),

H= NI/l ampere per metre

where l stands for the mean length of the flux path in metres.

Thus mmf =NI= Hl amperes.

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Transistor classification

This tutorial is about the kinds of transistors in which they are available. There are 2 main classifications of transistors. These two main classes are bipolar and field effect. Transistors are also classified on the basis of the semiconductor material used silicon or germanium, and also on the basis of their field of application (for example,general purpose, switching, high frequency, and much more). Transistors are also classified on the grounds of their application for which they are designed for. Table below shows the various categories of tansistors.

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Introduction to batteries

A battery is a useful device widely used to convert chemical energy into electricity. If we place an electric appliance in between its terminals the current produced will power the device. Battery is an indispensable item for many electronic devices and it is essential for devices that require power when no mains power is available. For example, without the battery, there would be no question of mobile phones or laptop computers.

The battery was invented 200 years back and these batteries are found almost everywhere in consumer and industrial products. Some common and practical examples where batteries are used include:

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Hysteresis loss

A disturbance in the alignment of the domains, referred as groups of atoms, of ferro-magnetic material give rise to energy to be expended in taking it through a cycle of magnetization. This energy acts as heat in the specimen and is known as the hysteresis loss. The amount of energy loss associated with hysteresis is proportional to the area of the hysteresis loop.The area of a hysteresis loop greatly depends on the type of material. The area, and thus the energy loss, is very bigger for hard materials than for soft type materials.

Diagram below shows typical hysteresis loops for:

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Hysteresis loop

Suppose a ferromagnetic material which is in a complete demagnetized state, i.e. one in which B = H = 0 be subjected to increasing magnetic field strength H and the corresponding flux density B measured. The diagram below shows resulting relationship between B and H on the the curve Oab. At a particular value of H, shown as Oy, it becomes very inconvineint to increase the flux density any more. The material is said to be saturated. Thus b_y is the point of saturation flux density.

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Field effect transistors

We can find Field effect transistors in 2 basic forms; junction gate & insulated gate. The gate source junction of a junction gate field effect transistor (JFET) is well a reverse-biased p-n junction.The gate connection of an insulated gate field effect transistor(IGFET), on the other end is insulated from the channel and charge is capacitively coupled to the channel. To keep matter simple, only JFET devices are considered in this tutorial. Diagram below presents the basic structure of an n-channel JFET.

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Electric current and quantity of electricity

Every atom is composed of protons, neutrons and electrons. The protons bears positive electrical charge, there is no electrical charge on the neutrons. Both protons and neutrons are contained within the nucleus which is in the center of the item. Electrons are not found in the nucleus, which bears a minute negatively electrical charge.

 Atoms of different materials are different from wachother by having different numbers of protons, neutrons and electrons. An atom would be electrically balanced if it has an equal number of protons and electrons, as we know that the positive and negative charges cancel each other out. When there are more than 2 electrons in an atom the electrons are arranged into shells and these shells are at various distances from the nucleus.

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Composite series magnetic Circuit

For a series magnetic circuit having n parts, the total reluctance S is given by the following series of reluctances:

S=S1+S2+· · ·+Sn

(This is just like the resistors that are connected in series in an electrical circuit.)

The problems illustrated below will make h concept more clear.

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Bipolar junction Transistors (BJT)

The Bipolar transistors normally made up of n-p-n or p-n-p junctions of either silicon (Si) or germanium (Ge) material. These junctions are, in fact, produced in a single slice of silicon by diffusing impurities through a photo graphically reduced mask. Silicon transistors are work better when compared with germanium transistors in the wide-spread majority of applications (mainly at high levels of temperature) and thus germanium devices are very rarely encountered in modern electronic equipment.The construction of typical n-p-n and p-n-p transistors is shown in diagrams 12.1 and 12.2. For conducting the heat away from the junction (important in medium and other high-power applications) the collector is allied with the metal case of the transistor.

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