Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance...
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Transcript of Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance...
![Page 1: Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance Related educational modules: –Sections 1.1, 1.2, 1.3.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551a8cfa550346e0158b4f66/html5/thumbnails/1.jpg)
Lecture 2
•Review Passive Sign Convention•Power Generation, Absorption•Power Sources•Resistance•Related educational modules:
–Sections 1.1, 1.2, 1.3
![Page 2: Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance Related educational modules: –Sections 1.1, 1.2, 1.3.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551a8cfa550346e0158b4f66/html5/thumbnails/2.jpg)
Passive sign convention – review• Passive sign convention:
• For passive circuit elements, we assume that the current enters the node with the higher voltage potential
• Your analyses will not be reliable unless you do this correctly
• Examples:
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Subscript notation can denote voltage polarity• Voltage polarity is sometimes indicated by subscript
notation• The order of the subscripts indicates the polarity
• The first subscript indicates assumed higher-voltage node• The second subscript is the assumed lower-voltage node
Note:
vBA = -vAB
![Page 4: Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance Related educational modules: –Sections 1.1, 1.2, 1.3.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551a8cfa550346e0158b4f66/html5/thumbnails/4.jpg)
“Ground”• Voltages are often represented as relative to
“ground”:• Ground (symbol: ) is a reference voltage; often 0V• Voltages relative to ground generally not called a voltage
difference; they are a difference relative to zero volts• Voltages relative to ground often represented with a single
subscript
![Page 5: Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance Related educational modules: –Sections 1.1, 1.2, 1.3.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551a8cfa550346e0158b4f66/html5/thumbnails/5.jpg)
Power Generation and Dissipation
• Circuit elements can either dissipate or generate power
• Power is dissipated (or absorbed) if current enters the positive voltage node
–
• Power is generated (or supplied) if current enters the negative voltage node
![Page 6: Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance Related educational modules: –Sections 1.1, 1.2, 1.3.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551a8cfa550346e0158b4f66/html5/thumbnails/6.jpg)
Power Generation and Dissipation• Power = voltagecurrent (p= vi)
• Power is absorbed if the power is positive (voltage and current are consistent with the passive sign convention)
• Power is generated if the power is negative (voltage and current not consistent with the passive sign convention)
6W absorbed 6W generated
![Page 7: Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance Related educational modules: –Sections 1.1, 1.2, 1.3.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551a8cfa550346e0158b4f66/html5/thumbnails/7.jpg)
Examples
• Determine the power absorbed by the circuit element below.
• The circuit element absorbs 10W. Determine the current in the element.
![Page 8: Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance Related educational modules: –Sections 1.1, 1.2, 1.3.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551a8cfa550346e0158b4f66/html5/thumbnails/8.jpg)
Power Supplies
• Power supplies provide a source of electrical power
• Conceptual types of power supplies (models of physical supplies):• Voltage, current sources• Independent, dependent sources• Ideal and non-ideal sources
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Independent voltage sources• Common symbols:
• Independent voltage sources maintain specified voltage, regardless of the current
![Page 10: Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance Related educational modules: –Sections 1.1, 1.2, 1.3.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551a8cfa550346e0158b4f66/html5/thumbnails/10.jpg)
Independent voltage sources – continued
• Voltage-current characteristic for constant voltage source:
i
VS
Power generated when current is
negative
Power absorbed when current is
positive
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Independent current sources
• Common symbol:
• Independent current sources maintain specified current, regardless of the voltage
![Page 12: Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance Related educational modules: –Sections 1.1, 1.2, 1.3.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551a8cfa550346e0158b4f66/html5/thumbnails/12.jpg)
Independent current sources – continued
• Voltage-current characteristic for constant current source:
IS
v
i
Power generated when voltage is
positive
Power absorbed when voltage is
negative
![Page 13: Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance Related educational modules: –Sections 1.1, 1.2, 1.3.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551a8cfa550346e0158b4f66/html5/thumbnails/13.jpg)
Ideal power sources – limitations
• Ideal sources can provide infinite power• Voltage sources provide specified voltage, regardless of
the current current can be infinite power can be infinite
• Current sources provide specified current, regardless of the voltage voltage can be infinite power can be infinite
• These models can be unrealistic• We will examine more realistic power source models
later
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Dependent Power Supplies• Some active circuit elements can be modeled as
dependent power sources• The current or voltage delivered by the source is
controlled by a current or voltage somewhere else in the circuit
• Four possible combinations• Voltage controlled voltage source (VCVS)• Current controlled voltage source (CCVS)• Voltage controlled current source (VCCS)• Current controlled current source (CCCS)
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Dependent Power Supplies – continued
• Examples:
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Resistors• Circuit symbol:
• R is the resistance• Units are ohms ()
• Voltage-current relation (Ohm’s Law):
)t(iR)t(v
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Resistors – continued
• Notes:• Resistors can only dissipate energy • The voltage-current relation is algebraic
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Resistor Power Dissipation• Ohm’s Law:
• Power:
• Combining:
)t(iR)t(v R
)t(v)t(i
)t(i)t(v)t(p
R
)t(v)t(v)t(p
R
)t(v)t(p
2
)t(Ri)t(p 2)t(Ri)t(i)t(p
![Page 19: Lecture 2 Review Passive Sign Convention Power Generation, Absorption Power Sources Resistance Related educational modules: –Sections 1.1, 1.2, 1.3.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551a8cfa550346e0158b4f66/html5/thumbnails/19.jpg)
Example
• Determine the power (generated or absorbed) by the resistor below:
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Conservation of energy
• In an electrical circuit, the power generated is the same as the power absorbed
• Slightly more mathematically,
• Recall that power absorbed is positive and power generated is negative
0elements All
p
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Conservation of power – example• Determine the power (absorbed or generated) by the
voltage source VS