ELECTRO NOTES
INTRODUCTION TO DC
Direct current → unidirectional flow of electric charge (from + to - in circuits, but in reality it’s from - to +)
Ohm’s law → 𝑉 = 𝐼𝑅
Power → 𝑃 = 𝑉𝐼
Resistance →
● series (line) constant current
(𝑅𝑒𝑞 = 𝑅 + 𝑅2)
1
● parallel (sandwich) constant voltage
𝑅1*𝑅2
(𝑅𝑒𝑞 = 𝑅1+𝑅2
)
● short circuit (lonely) cancels out
(always dissipating)
Sources →
● voltage source (provides EMF needed to drive electric current in a circuit)
● current source (provides consistent flow of electrons to a circuit)
(can provide or dissipate)
Dividers →
𝑅
● current: 𝐼𝑖 = 𝐼𝑇( 𝑅 +𝑅
2
)
1 2
𝑅
● voltage: 𝑉𝑜𝑢𝑡 = 𝑉𝑖𝑛( 𝑅 +𝑅
2
)
1 2
, LINEAR CIRCUIT ANALYSIS
Superposition theorem →
1. divide circuit in as many power sources as you have and cancel the rest
a. short-circuit voltages
b. open-circuit currents
2. add resulting voltages and resulting currents
(beware of direction)
Kirchhoff’s current law (I) → nodes
1. identify nodes
2. choose ground (be smart)
3. assign directions
∆𝑉
4. write equations (all equal 0 or one equals others) in terms of Ohm’s law ( 𝑅
)
a. if no resistance, leave name
b. if current source, that’s it
Kirchhoff’s voltage law (II) → loops
1. identify loops
2. assign polarities (current direction and voltage drops)
3. write equations (second element always, from + to -)
4. solve for unknowns
Thevenin and Norton →
1. identify and isolate load resistor
2. find 𝑅𝑡ℎ /𝑅𝑛 by canceling power sources and finding 𝑅𝑒𝑞 (load included)
● find 𝑉𝑡ℎ through any other method
● find 𝑉𝑛 through short-circuiting A and B and use any other method (load considered)
3. find 𝐼𝑡ℎ through Ohm’s law if needed
● TH: draw equivalent circuit with points A and B, and 𝑉𝑡ℎ in series with 𝐼𝑡ℎ
● N: draw equivalent circuit with points A and B, and 𝐼𝑛 in parallel with load resistor
INTRODUCTION TO DC
Direct current → unidirectional flow of electric charge (from + to - in circuits, but in reality it’s from - to +)
Ohm’s law → 𝑉 = 𝐼𝑅
Power → 𝑃 = 𝑉𝐼
Resistance →
● series (line) constant current
(𝑅𝑒𝑞 = 𝑅 + 𝑅2)
1
● parallel (sandwich) constant voltage
𝑅1*𝑅2
(𝑅𝑒𝑞 = 𝑅1+𝑅2
)
● short circuit (lonely) cancels out
(always dissipating)
Sources →
● voltage source (provides EMF needed to drive electric current in a circuit)
● current source (provides consistent flow of electrons to a circuit)
(can provide or dissipate)
Dividers →
𝑅
● current: 𝐼𝑖 = 𝐼𝑇( 𝑅 +𝑅
2
)
1 2
𝑅
● voltage: 𝑉𝑜𝑢𝑡 = 𝑉𝑖𝑛( 𝑅 +𝑅
2
)
1 2
, LINEAR CIRCUIT ANALYSIS
Superposition theorem →
1. divide circuit in as many power sources as you have and cancel the rest
a. short-circuit voltages
b. open-circuit currents
2. add resulting voltages and resulting currents
(beware of direction)
Kirchhoff’s current law (I) → nodes
1. identify nodes
2. choose ground (be smart)
3. assign directions
∆𝑉
4. write equations (all equal 0 or one equals others) in terms of Ohm’s law ( 𝑅
)
a. if no resistance, leave name
b. if current source, that’s it
Kirchhoff’s voltage law (II) → loops
1. identify loops
2. assign polarities (current direction and voltage drops)
3. write equations (second element always, from + to -)
4. solve for unknowns
Thevenin and Norton →
1. identify and isolate load resistor
2. find 𝑅𝑡ℎ /𝑅𝑛 by canceling power sources and finding 𝑅𝑒𝑞 (load included)
● find 𝑉𝑡ℎ through any other method
● find 𝑉𝑛 through short-circuiting A and B and use any other method (load considered)
3. find 𝐼𝑡ℎ through Ohm’s law if needed
● TH: draw equivalent circuit with points A and B, and 𝑉𝑡ℎ in series with 𝐼𝑡ℎ
● N: draw equivalent circuit with points A and B, and 𝐼𝑛 in parallel with load resistor
