Basic 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 