0. ECE 1270: Introduction to Electric Circuits
Lecture 4:
Equivalent Networks
Chapter 3
Simple Resistive Circuits

1. Resistors in Series
Req=equivalent resistance

2. Resistors in Series
Req=equivalent resistance

3. Resistors in Parallel
Req=equivalent resistance

4. Example 3.1: Find is, i1, i2
3+6=9 in parallel with 18, Find parallel combo of 18||9=6 Now, Is=120/10=12A. Define V1 across 6 ohm. Then V1=Is*6=72V
Find I1=V1/18 = 4A, I2=V1/9=8A.

5. AP 3.1 (a) Find the voltage v
(b) power delivered the to the circuit the current source
(c) power disspated in the 10 Ω resistor

6. Voltage Divider Circuit
Formulas for V1 and V2

7. Voltage Divider Examples

8. Current Divider Circuit
Formulas

9. Current Divider Examples
Example 3.3: Find power dissipated in 6 Ω resistor
AP 3.3: Find R such that 4 A will flow through 80 Ω resistor

10. How do you measure Current and Voltage in a circuit?
Use Ammeter to measure the current: connect it in series
Use Voltmeter to measure the voltage: connect it in parallel

11. Delta-to-Y (Pi-to-Tee) Equivalent Circuits
Delta or Pi Configuration
Y or Tee Configuration

12. Delta-to-Y Transformation
Example 3.7: Find power supplied by 40V source
Wheatstone Bridge

13. How do you measure Resistance?
Wheatstone Bridge
The example 3.7 is a wheatstone bridge, which is used to measure resistance
When the bridge is balanced, ig=0 and i1=i3 and i2=ix
Then, Rx/R3=R2/R1
If R2=R1 then Rx=R3

14. Y-to-Delta Transformation
AP3.8: Use Y-to-Delta transformation to find v