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Published byAndrew Kelly Modified over 5 years ago

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Objective of Lecture Provide step-by-step instructions for mesh analysis, which is a method to calculate voltage drops and mesh currents that flow around loops in a circuit. Chapter 3.4 and Chapter 3.5

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Mesh Analysis Technique to find voltage drops around a loop using the currents that flow within the loop, Kirchoff’s Voltage Law, and Ohm’s Law First result is the calculation of the mesh currents Which can be used to calculate the current flowing through each component Second result is a calculation of the voltages across the components Which can be used to calculate the voltage at the nodes.

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Definition of a Mesh Mesh – the smallest loop around a subset of components in a circuit Multiple meshes are defined so that every component in the circuit belongs to one or more meshes

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Steps in Mesh Analysis V in

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Step 1 Identify all of the meshes in the circuit V in

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Step 2 Label the currents flowing in each mesh i1i1 i2i2 V in

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Step 3 Label the voltage across each component in the circuit i1i1 i2i2 +V1_+V1_ V in +V3_+V3_ +V5_+V5_ +V6_+V6_ + V 2 - + V 4 -

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Step 4 Use Kirchoff’s Voltage Law i1i1 i2i2 +V1_+V1_ V in +V3_+V3_ +V5_+V5_ +V6_+V6_ + V 2 - + V 4 -

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Step 5 Use Ohm’s Law to relate the voltage drops across each component to the sum of the currents flowing through them. Follow the sign convention on the resistor’s voltage.

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Step 5 i1i1 i2i2 +V1_+V1_ V in +V3_+V3_ +V5_+V5_ +V6_+V6_ + V 2 - + V 4 -

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Step 6 Solve for the mesh currents, i 1 and i 2 These currents are related to the currents found during the nodal analysis.

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Step 7 Once the mesh currents are known, calculate the voltage across all of the components.

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12V

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From Previous Slides

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Substituting in Numbers

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Substituting the results from Ohm’s Law into the KVL equations

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Chugging through the Math One or more of the mesh currents may have a negative sign. Mesh Currents ( A) i1i1 740 i2i2 264

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Chugging through the Math Voltage across resistors (V) V R1 = -i 1 R 2 -2.96 V R2 = i 2 R 2 5.92 V R3 =(i 1 – i 2 ) R 3 2.39 V R4 = i 2 R 4 1.59 V R5 = (V 4 – V 5 )0.804 V R6 = (V 5 – 0V)0.740 The magnitude of any voltage across a resistor must be less than the sum of all of the voltage sources in the circuit In this case, no voltage across a resistor can be greater than 12V.

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Chugging through More Math Currents ( A) I R1 = i 1 740 I R2 = i 1 740 I R3 = i 1 - i 2 476 I R4 = i 2 264 I R5 = i 2 264 I R6 = i 1 740 I Vin = i 1 740 The currents through each component in the circuit.

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Check None of the mesh currents should be larger than the current that flows through the equivalent resistor in series with the 12V supply.

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Summary Steps in Mesh Analysis 1. Identify all of the meshes in the circuit 2. Label the currents flowing in each mesh 3. Label the voltage across each component in the circuit 4. Write the voltage loop equations using Kirchoff’s Voltage Law. 5. Use Ohm’s Law to relate the voltage drops across each component to the sum of the currents flowing through them. 6. Solve for the mesh currents 7. Once the mesh currents are known, calculate the voltage across all of the components.

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