A three-phase supply is generated when three coils are placed 120° apart and the whole rotated in a uniform magnetic field as shown in Fig (a). The result is three independent supplies of equal voltages which are each displaced by 120° from each other as shown in Fig (b). The convention adopted to identify each

There are a number of situations when digital signals have to be converted to analogue ones. For example, a digital computer often needs to produce a graphical display on the screen; this involves using a D/A converter to change the two-level digital output voltage from the computer, into a continuously varying analogue voltage for the

If both inputs of the op amp shown in Fig. 1 are used simultaneously, then from equation, the output voltage is given by: Vo = Ao(V2 − V1) When V2 > V1 then Vo is positive, its maximum value being the positive supply voltage + Vs, which it has when (V2 > V1) ≥ Vs/Ao.

Operational Amplifiers (usually called ‘op amps’) were originally made from discrete components, being designed to solve mathematical equations electronically, by performing operations such as addition and division in analogue computers. Now produced in integrated-circuit (IC) form, op amps have many uses, with one of the most important being as a high-gain d.c. and a.c. voltage

Networks in which electrical energy is fed in at one pair of terminals and taken out at a second pair of terminals are called two port networks. The network between the input port and the output port is a transmission network for which a known relationship exists between the input and output currents and voltages.

The maximum power transfer theorem states: The power transferred from a supply source to a load is at its maximum when the resistance of the load is equal to the internal resistance of the source. Hence, in Fig when R = r the power transferred from the source to the load is a maximum. Typical

Table summarises the characteristics of some typical bipolar junction transistors for different applications, where IC max is the maximum collector current, VCE  max is the maximum collector – mitter voltage, PTOT max is the maximum device power dissipation, and hfe is the typical value of common-emitter current gain. Transistor characteristics and maximum ratings Device Type IC max

Bipolar junction transistors generally comprise n-p-n or p-n-p junctions of either silicon (Si) or germanium (Ge) material. The junctions are, in fact, produced in a single slice of silicon by diffusing impurities through a photographically reduced mask. Silicon transistors are superior when compared with germanium transistors in the vast majority of applications (particularly at high

Arsenic, antimony and phosphorus have five valency electrons and when a semiconductor is doped with one of these substances, some impurity atoms are incorporated in the tetrahedral structure. The ‘fifth’ valency electron is not rigidly bonded and is free to conduct, the impurity atom donating a charge carrier. Indium, aluminium and boron have three valency

When a conductor is moved across a magnetic field so as to cut through the lines of force (or flux), an electro motive force (e.m.f) is produced in the conductor. If the conductor forms part of a closed circuit then the e.m.f produced causes an electric current to flow round the circuit. Hence an e.m.f