Page 1 :
' SOURCE OF ELECTRICAL ENERGY, , There are two types of sources of electrical energy, ideal voltage source and, ideal currrent source., , An ideal voltage source is two-terminal element which maintains a terminal voltage v(t) regardless of the value of the current through its terminals, as, shown in Fig. 1.6 (a) and (b). It is customary to take the associated current, direction as flowing out of the positive terminal. A v-i plot of the terminal, voltage—current relationship, for an ideal voltage source, is shown in Fig. 1.6, (c). At any instant, the value of the terminal voltage is a constant with respect, to the current value ¢. Whenever v == 0, the voltage source is the same as that, of a short circuit. Symbolic representation of dependent or controlled voltage, source is in Fig. 1.6(d)., , In a practical voltage source, the voltage across the terminals of the souree, keeps falling as the current through it increases, as showa in Fig. 1.7. This
Page 2 :
EES NATE GED Mah CTE TED PY GVO FUTIiG AT, , n be explained by putting a resistance in series with an ideal volt, , paviour C80, in Fig. 1.7(a). Then we have the terminal voltage v, as, as, , age gource, aS, wi=Vv—ir, : (27), , leila, , e i, is the current flowing and r the internal resistance of the ideal voltage, , , , , , , , , , , , j when, 1 gourve of voltage ¥. The practical voltage source, | oie in the lisnit 7 edamaltiiethere e approaches the ideal voltage, vA, a(t) i, ——O, a, +, v(t) a, =f =, 0 t, (a) (d) {c), -——0, » v(x!, LO, (@), Fig. 1.6. (a-c) Ideal independent voltage source and y—/ characteristics, n of dependent voltage source, , (d) symbolic representatio, , i, ir, , re +, u(t) % v %, —_————9, , , , (5), , (a), oltage source and y-i characteristic, , Fig. 1.7. Practical v, , -terminal element which maintains a cut, ardless of the value of the terminal, , An ideal current source is a (we, sentation of dependent or, , rent i(t) flowing through its terminals reg, voltage, as shown in Fig. 1.8(a)- The symbolic repre
Page 3 :
18 NETWORKS AND SYSTEMS, , oe current source is in Fig. 1.8(c). The associated current-voltage sign, , : ion is such that the current flows out of the terminal marked +, i.e., along the direction of the arrow. The current flowing in the external circuit is, connected to the active source from positive to negative. The v-i characteristic, of an ideal current source is shown in Fig. 1.8(b), which at any instant is simply, , a vertical line. When J = 0, the ideal current source has the same y~/ characteristic as an open circuit., , v, +, u(t) vit), 6 1 t, , f(x), (a) (b) (e), , Fig. 1.8, (ab) Ideal current sou, , v-i characteristic. (c) symbolic representation, of dependent or col, , -d current source, , , , , , In a practical current source, {..c Current through the source decreases as }, the voltage across it increases, as shown in Fig. 1.9(b). This behaviour can be, explained by putting a resistance across the terminals of the source, as in, Fig. 1.9(a). Then the terminal current is given by, , , , i, i, , (28), , where & is the internal resistance of the ideal current source., , uf, , , , (a) (6), , Fig. 1.9. Practical current source and v-f characteristic, , The practical current source approaches the ideal current source m the, it cect infinity. The current und veltage tp the active element {source}, limit R bec j, , re in the same direction whereas they are in eEpposiiog in passive element, ie, are » $a
Page 4 :
: scmreat is increasing for rising Voltage in the active, , the ;, ~ gurrent and voltage are of opposite direction in passive, , known as independent sources. Dependent or c, following types:, , to ses eee ae, , (i) Voltage controlled voltage source (VCVS) as in Fig. 1.10(a, : (ii) Current controlled voltage source (CQVS) as in Fig er, , (iii) Voltage controlled current source (VCCS) as in Fig. 1.10(c), , (iv) Current controlled current source (CCOCS) as in Fig. 1.10(d), , f The terminal voltage of a dependent or controlled voltage source, Fig., 1,10(a-b) is a specified function of some variable x, usually a current or voltage, in the circuit, i.c., v=v(x), regardless of the current flowing through the source., Similarly, the current supplied by a dependent or controlled current source,, , Fig. 1.10(c-d), will be i = i(x), regardless of the terminal voltage., , 1:0 lz pig!, , +, , , , , , (b), (a), , (a), , controlled) sources, , , , Dependent (, «@) ccecs, , Sty, , iz, , clement whereas, element, :, , Controlled sources: The voltage and Current sources discussed above are, Ontrolled sources are of the
