Chapter 6 Series –Parallel Circuits A simple series-parallel circuit Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. R4 is added to the circuit in series with R1. Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. R5 is added to the circuit in series with R2. Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. R6 is added to the circuit in parallel with the series combination of R1 and R4. Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Illustration of voltage relationships. Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Balanced (Calibrated) Wheatstone bridge when the shows 0V and 0 A Between A and B Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e •Used in Sensitive Measurement Instruments (Strain, Temperature, Etc.) •Converts Change in Transducer Resistance (RX) to a Voltage Output (VA-B) •Voltage Output Sent to Amplifier, Conversion and Readout Circuits •RV is Used to Calibrate VAB to 0V at Known Rx Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Wheatstone Bridge VOUT = 0V (Calibrated) When: •R1/R3 = R2/R4 Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Using a Transducer Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e VA = (1K Ohm/1.9K Ohm) 12V = 6.32V VB = 6V VA – B = 6.32V – 6V = 320mV Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Example of a more complex Wheatstone Load Cell Calibration is done in a downstream Circuit Loading Effect RL in parallel with R2 Creates: •More Current Through R1 •More Voltage Drop Across R1 •Lower voltage at VOUT Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The effect of a load resistor. RL 10 Times Larger Than R2 Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. VOUT Unloaded =(10K Ohms /14.4K Ohms) 5V = 3.5V Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. VOUT Unloaded =(10K Ohms /14.4K Ohms) 5V = 3.5V VOUT = (5K Ohms/9.7K Ohms) 5V = 2.6V Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e VOUT = (9.1K Ohms/13.8K Ohms) 5V = 3.4V Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Maximum Power Transfer – Impedance Matching Load Maximum power is transferred to the load when RL = RS. Maximum Power Transfer: Common Application Output of Audio Amplifier Impedance Matched with Speaker Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. In this case, Maximum power is transferred to the load when RL = 75 Ohms Load 75 Ohms •The Source “Sees” a 75 Ohm Load •The Load “Sees” a 75 Ohm Source Maximum Power Transfer RL = 0 Ohms VRL = 0V IRL = 0A PRL = 0W RL = 25 Ohms VRL = 2.5V IRL = 100mA PRL = 250mW RL = 75 Ohms VRL = 5V IRL = 67mA PRL = 335mW Curve showing that the load power is maximum when RL = RS Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e RL = 125 Ohms VRL = 6.25V IRL = 50mA PRL = 313mW Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The general form of a Thevenin equivalent circuit is a voltage source in series with a resistance. Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Example of the simplification of a circuit by Thevenin’s theorem. Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Superposition – Determining Current from Two Sources Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e RT = 150 Ohms IT = 66.7mA IR2(Vs2) = 33.4mA Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 3. Replace VS1 With a Short 4. Calculate IR2 Created From VS2 Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e RT = 150 Ohms IT = 33.3mA IR2 (Vs2) = 16.7mA Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 5. Calculate IR2 as Algebraic Sum of Previous Calculations IR2(Total) = |33.4mA -16.7mA| = 16.7mA Thomas L. Floyd Electronics Fundamentals, 6e Electric Circuit Fundamentals, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Troubleshooting 1 Should be 4.22V Fault – R2 Open Troubleshooting 2a Should be 4.22V Fault – R2 Open Troubleshooting 2b Fault – R2 Open Troubleshooting 3 Correct Value Should be 13.8V Fault – R7 Shorted
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