[기초회로이론] Chap 02 - Circuit Elements

📣 Disclaimer : Dorf’s Introduction to Electric Circuits Global Ed. 를 바탕으로 작성된 정리입니다

2.2 Engineering Linear Models

• A linear element satisfies the properties of both superposition and homogeneity
• superposition : if $i_1 \rightarrow v_1$ / $i_2 \rightarrow v_2$, it is necessary that the exitation $i_1+i_2$ will provide $v_1+v_2$.
• homogeneity (Scalability) : $i\rightarrow v$, $ki\rightarrow kv$
• Linearity does not necessarily mean 1st order polynomial

2.3 Active and Passive Circuit Elements

• Passive element : consumes energy (absorbs)
• Active element : supplies energy
• Same convention of sign of when we considered before

2.4 Resistors

• Always passive element (can be active if and only if R<0 but it is impossible).

\[R={\rho L \over A}\]

defined as constant resistance R, as Ohm’s Law, $v=Ri$, as we all know.

• Ohm’s law only applies at Ohmic substances
• Resistance (ratio of V over i) slightly increases on AC current because in higher frequency, electrons tend to move on the surface of the conductor which decreases effective area A
• siemens (S) : Ohm’s law can also be written as : $i=Gv$, where $G$ is conductance (or mhos, inverted $\Omega$ symbol but seldomly used.
• $G={1\over R}$

2.5 Independent Sources

• voltage or current independent source is a generator not dependent on other circuit variables.

  

• Independent voltage source. $i(t)$can be $-\infty$ to $+\infty$

  

Independent current source. $v(t)$ can be any value.

Every independent source is ideal, conceptual.

• Some batteries can be modeled as independent voltage source within certain conditions (small range of current)

• Short circuit(Closed) : Special case of ideal voltage source (no resistance)

  

• Open circuit : Special case of ideal current source ($v(t)$can be any value)

  

2.6 Voltmeters and Ammeters

• in case of ideal ammeter and voltmeter, it can be considered as ideal short / open circuit, respectively.
• Black (or dark) pole denotes the ‘minus’ polarity

2.7 Dependent Sources

• Voltage or current of one circuit element is proportional to volt or current of second circuit element.

  

CCCS, VCVS, VCCS, CCVS

• for some three-terminal element can be dissected (or interpreted) with combination of two-terminal elements including dependent sources.

2.8 Resisitive Transducers

• transducers convert physical quantities to electrical quantities. (a.k.a. sensor)

2.9 Switches

• SPST(Single pole single throw) switch : open / close state
• SPDT(Single pole double throw) switch : Break before make, Make before break switches

• make before break switch is often used when circuit is not defined when the switch passes thru.