Page 15 - Basics of Electrical, Electronic and Communication

1.7. Open circuit voltage and short circuit current 11

IS RS RL

Figure 1.9: Real current source

1.7 Open circuit voltage and short circuit current

Consider any circuit with two output terminals A and B (Figure 1.10(a)).
The open-circuit voltage V oc across terminals A and B is the voltage
which appears with nothing connected between them. i.e., R AB = ∞
A
A
Circuit
Circuit VOC ISC
B B
(a) Open circuit (b) Short circuit

Figure 1.10: Open circuit and short circuit

In the circuit shown in Figure 1.10(b) terminals A and B are con-
nected together with a piece of wire i.e., zero resistance, then the short-
circuit current is the current that flows through the wire. Short circuit
current I SC is that current which flows between two terminals when
they are shorted. i.e., R AB = 0.

Example 1
A resistor of 5 Ω is connected in series with a parallel combination of
6 Ω and 3 Ω. Find the supply current taken from a 35 V dc source.

Solution
Let R P be the equivalent resistance of the parallel combination
of 3 Ω and 6 Ω.

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