1 Chapter 2 Resistive circuits EMLAB Contents 2

1 Chapter 2. Resistive circuits EMLAB

Contents 2 1. Ohm’s law 2. Kirchhoff’s laws 3. Series and parallel resistor combinations 4. Y-Δ transformation 5. Circuits with dependent sources EMLAB

Resistors : microscopic view 3 nucleus electrons Entering resistive material, charges are decelerated, which decrease current flow. EMLAB

Types of resistors 4 (1), (2), and (3) are high power resistors. (4) and (5) are high-wattage fixed resistors. (6) is a high precision resistor. (7)–(12) are fixed resistors with different power ratings. EMLAB

1. Ohm’s law 5 resistance ; conductance Power absorption : EMLAB

Example 2. 1 6 Determine the current and the power absorbed by the resistor. EMLAB

Glossary (1) Node 7 A node is simply a point of connection of two or more circuit elements. node Although one node can be spread out with perfect conductors, it is still only one node EMLAB

8 (2) loop (3) branch A loop is simply any closed path through the circuit in which no node is encountered more than once a branch is a single or group of components such as resistors or a source which are connected between two nodes EMLAB

2. Kirchhoff’s law 9 (1) Kirchhoff ’s current law (KCL) : the algebraic sum of the currents entering(out-going) any node is zero → the sum of incoming currents is equal to the sum of outgoing currents. (2) Kirchhoff’s voltage law (KVL), the algebraic sum of the voltages around any loop is zero EMLAB

Kirchhoff’s Current law 10 R 2 R 1 R 3 Current definition • The direction of a current can be chosen arbitrarily. • The value of a current can be obtained from a voltage drop along the direction of current divided by a resistance met. R EMLAB

Kirchhoff’s Voltage law 11 Sum of voltage drops along a closed loop should be equal to zero! R 1 C 1 Voltage convention EMLAB

Example 2. 6 12 Find the unknown currents in the network. Node 1 : Node 2 : Node 3 : Node 4 : Node 5 : EMLAB

Example E 2. 6 13 Find the current ix in the circuits in the figure. EMLAB

Example E 2. 8 14 Find Vad and Veb in the network in the figure. EMLAB

Example 2. 15 15 Given the following circuit, let us find I, Vbd and the power absorbed by the 30 kΩ resistor. Finally, let us use voltage division to find Vbc. EMLAB

Series resistors 16 equivalent EMLAB

Parallel resistors 17 equivalent EMLAB

Example 2. 19 18 Given the circuit, we wish to find the current in the 12 -kΩ load resistor. equivalent EMLAB

Example 2. 20 19 We wish to determine the resistance at terminals A-B in the network in the figure. EMLAB

Y-Δ transformation 20 Δ Y equivalent EMLAB

21 -+ -+ EMLAB

Example 2. 26 22 Given the network in Fig. 2. 36 a, let us find the source current IS. EMLAB

2. 8 Circuits with dependent sources 23 Example 2. 27 Let us determine the voltage Vo in the circuit in the figure. EMLAB

Example 2. 28 24 Given the circuit in the figure containing a current-controlled current source, let us find the voltage Vo. EMLAB

Example 2. 30 25 An equivalent circuit for a FET common-source amplifier or BJT common-emitter amplifier can be modeled by the circuit shown in the figure. We wish to determine an expression for the gain of the amplifier, which is the ratio of the output voltage to the input voltage. GND can be arbitrarily set. EMLAB

Transistor amplifier 26 Transistor EMLAB

2. 10 Application examples 27 Example 2. 33 : The Wheatstone bridge circuit. EMLAB