Basic Circuit Theory

Yong Heui Cho @ Mokwon University

Some of slides are referred to:[1] jerbor, Circuit theory mt, slideshare, 2011.

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Electronic Circuits

1. Semiconductor & Electronic Ckts2. Introduction to Smart Sensors3. Basic Circuit Theory

4. Diode – Operational Princi-ple

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Electric Circuit• An interconnection of electrical

elements.

□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

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Charge (Q) & Current (I)• Electric current is the time rate of

change of charge, measured in am-peres (A).

• Direct Current (DC) is a current that re-mains constant with time.

• Alternating Current (AC) is a current that varies sinusoidally with time.

□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

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Voltage (V)• Voltage (or potential difference) is the energy

required to move a unit charge through an ele-ment, measured in volts (V).

• Voltage vab between two points a and b in an electric circuit is the energy (or work) needed to move a unit charge from a to b; mathematically,

□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

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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 VIP21

av

timePE

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Sign Convention• Passive sign convention is satisfied when the

current enters through the positive terminal of an element and p = +vi. If the current en-ters through the negative terminal, p = −vi.

□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

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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.

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Ohm’s Law• Ohm’s law states that the voltage “v”

across a resistor is directly proportional to the current “i” flowing through the resistor.

• Short circuit is a circuit element with resis-tance approaching zero.

• Open circuit is a circuit element with resis-tance approaching infinity.

IRV

□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

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Current & Water

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Types of Resistors

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KVL• Kirchhoff Voltage Law

□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

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KCL• Kirchhoff Current Law

□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

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3 Laws for Analysis• Any circuits can be analyzed with

3 laws.–Ohm’s law– KVL– KCL– Just try and solve!

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Equivalent Resistor• Complicated resistor networks

can be replaced with one R.

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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 con-sisting of a voltage source VTh in series with a resistor RTh, where VTh is the open-circuit voltage at the termi-nals and RTh is the input or equivalent resistance at the terminals when the independent sources are turned off.

□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

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Norton Theorem• Developed by E. L. Norton, an American engineer

at Bell Telephone Laboratories in 1926, about 43 years after Thevenin published his theorem.

• Norton’s theorem states that a linear two-terminal circuit can be replaced by an equivalent circuit consisting of a current source IN in parallel with a resistor RN, where IN is the short-circuit current through the terminals and RN is the input or equiv-alent resistance at the terminals when the inde-pendent sources are turned off.

□ Courtesy to jerbor, Circuit theory mt, slideshare, 2011.

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Capacitor [F]• A component used to store elec-

tric charge CVQ

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Inductor [H]• A component used to generate

magnetic flux LI

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Impedance Z• AC resistance• Z = R + jX– Resistance (R) and reactance (X)

ZIV