This document provides an overview of basic circuit theory concepts. It defines key electrical terms like charge, current, voltage, power, and energy. It describes different circuit elements including resistors, capacitors, and inductors. It introduces important circuit analysis laws and theorems like Ohm's law, Kirchhoff's laws, and Thevenin's and Norton's theorems. The document uses diagrams and equations to illustrate electrical concepts and is intended to provide foundational knowledge of circuit theory.

1. Basic Circuit Theory
Yong Heui Cho @ Mokwon University
Some of slides are referred to:
[1] jerbor, Circuit theory mt, slideshare, 2011.

2. 2
Electronic Circuits
1. Semiconductor & Electronic Ckts
2. Introduction to Smart Sensors
3. Basic Circuit Theory
4. Diode – Operational Principle

3. 3
Electric Circuit
• An interconnection of electrical elemen
ts.
□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

4. 4
Charge (Q) & Current (I)
• Electric current is the time rate of change
of charge, measured in amperes (A).
• Direct Current (DC) is a current that remains c
onstant with time.
• Alternating Current (AC) is a current that varie
s sinusoidally with time.
□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

5. 5
Voltage (V)
• Voltage (or potential difference) is the energy re
quired to move a unit charge through an eleme
nt, measured in volts (V).
• Voltage vab between two points a and b in an ele
ctric circuit is the energy (or work) needed to m
ove a unit charge from a to b; mathematically,
□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

6. 6
Power & Energy
• Electric power [W]
– Rate at which electrical energy is
transferred by an electric circuit
– DC:
– AC:
• Energy [J]
–
– kWh: kW x hours
VIP 
VIP
2
1
av 
time PE

7. 7
Sign Convention
• Passive sign convention is satisfied when the cu
rrent enters through the positive terminal of an
element and p = +vi. If the current enters throu
gh the negative terminal, p = −vi.
□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

8. 8
Dependent Sources
• Four possible types of dependent sources
– Voltage-Controlled Voltage Source (VCVS)
– Current-Controlled Voltage Source (CCVS)
– Voltage-Controlled Current Source (VCCS)
– Current-Controlled Current Source (CCCS)
□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

9. 9
Ohm’s Law
• Ohm’s law states that the voltage “v” across a re
sistor is directly proportional to the current “i” f
lowing through the resistor.
• Short circuit is a circuit element with resistance
approaching zero.
• Open circuit is a circuit element with resistance
approaching infinity.
IRV 
□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

10. 10
Current & Water

11. 11
Types of Resistors

12. 12
KVL
• Kirchhoff Voltage Law
□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

13. 13
KCL
• Kirchhoff Current Law
□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

14. 14
3 Laws for Analysis
• Any circuits can be analyzed with 3 laws.
– Ohm’s law
– KVL
– KCL
– Just try and solve!

15. 15
Equivalent Resistor
• Complicated resistor networks can be
replaced with one R.

16. 16
Thevenin Theorem
• Developed in 1883 by M. Leon Thevenin (1857–1926), a
French telegraph engineer
• Thevenin’s theorem states that a linear two-terminal
circuit can be replaced by an equivalent circuit consis
ting of a voltage source VTh in series with a resistor RTh
, where VTh is the open-circuit voltage at the terminals
and RTh is the input or equivalent resistance at the ter
minals when the independent sources are turned off.
□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

17. 17
Norton Theorem
• Developed by E. L. Norton, an American engineer at B
ell Telephone Laboratories in 1926, about 43 years afte
r Thevenin published his theorem.
• Norton’s theorem states that a linear two-terminal cir
cuit can be replaced by an equivalent circuit consistin
g of a current source IN in parallel with a resistor RN, w
here IN is the short-circuit current through the termin
als and RN is the input or equivalent resistance at the t
erminals when the independent sources are turned of
f.
□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

18. 18
Capacitor [F]
• A component used to store electric
charge
CVQ 

19. 19
Inductor [H]
• A component used to generate magnetic
flux
LI

20. 20
Impedance Z
• AC resistance
• Z = R + jX
– Resistance (R) and reactance (X)
ZIV 