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Lecture 2: Circuit Elements and Series/Parallel Resistors Nilsson 2.1-2.5, 3.1-3.2. ENG17 (Sec. 1): Circuits I Summer 1 2014. June 24, 2014. Overview. Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws Dependent Sources Series / Parallel Resistors. - PowerPoint PPT Presentation
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Lecture 2:Circuit Elements and Series/Parallel ResistorsNilsson 2.1-2.5, 3.1-3.2
ENG17 (Sec. 1): Circuits I
Summer 1 2014
June 24, 2014
2
Overview
• Voltage & Current Sources
• Electrical Resistance• Circuit Model• Kirchhoff’s Laws• Dependent Sources• Series / Parallel
Resistors
3
5 Ideal Basic Circuit Elements
• Voltage Sources• Current Sources• Resistors• Inductors• Capacitors
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Schematics - GND
• Ground (GND) is a common connection• Typically connect to Earth GND• Always a zero [V] reference potential
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Overview
• Voltage & Current Sources
• Electrical Resistance• Circuit Model• Kirchhoff’s Laws• Dependent Sources• Series / Parallel
Resistors
14
Overview
• Voltage & Current Sources
• Electrical Resistance• Circuit Model• Kirchhoff’s Laws• Dependent Sources
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Overview
• Voltage & Current Sources
• Electrical Resistance• Circuit Model• Kirchhoff’s Laws• Dependent Sources• Series / Parallel
Resistors
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Kirchhoff’s Current Law (KCL)
The algebraic sum of all the currents at any node in a circuit equals zero.
Therefore:• Assign signs to currents at each node• Positive (+) for current leaving a node• Negative (-) for current entering a node• Or vice versa
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Kirchhoff’s Voltage Law (KVL)
The algebraic sum of all the voltages around any closed path in a circuit equals zero.
Therefore:• Assign signs to voltages in a loop• Positive (+) for voltage rise• Negative (-) for voltage drop• Or vice versa
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Observations
• 7 equations 4 equations– Because I and V are related
through R, we only need one
• With only 2 branches at a node (in series), we only need to know 1 current
𝑣1=𝑖1𝑅1
𝑣𝑐=𝑖𝑐𝑅𝑐
𝑣 𝑙=𝑖𝑙𝑅 𝑙
𝑖𝑠− 𝑖1=0𝑖1+𝑖𝑐=0−𝑖𝑐−𝑖𝑙=0𝑖𝑙−𝑖𝑠=0
𝑣 𝑙−𝑣𝑐+𝑣1−𝑣𝑠=0
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Overview
• Voltage & Current Sources
• Electrical Resistance• Circuit Model• Kirchhoff’s Laws• Dependent Sources• Series / Parallel
Resistors
28
Overview
• Voltage & Current Sources
• Electrical Resistance• Circuit Model• Kirchhoff’s Laws• Dependent Sources• Series / Parallel
Resistors
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Series Connected Elements
• Resistors in series carry the same current– KCL proves this
• Resistors in series can be summed– KVL proves this
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Parallel Connected Elements
• Resistors in parallel have same voltage across their terminals– KVL proves this
• Resistors in parallel can be summed inversely– KCL proves this– Conductances are summed