Tài liệu Malvino-EP-01-Introduction pdf

MALVINO Electronic Electronic PRINCIPLES SIXTH EDITION Introduction Introduction Chapter 1 Three kinds of formulas The definition: Invented for a new concept Q C = Q V {defines what capacitance is} {does not require verification} The law: Summarizes a relationship that exists in nature fK Q 1 Q 2 {ifidb i t} The derivation : Obtained by manipulating other f = K d 2 { ver ifi e d b y exper i men t} The derivation : Obtained by manipulating other formulas using mathematics Q=CV Q = CV An ideal voltage source maintains a constant An ideal voltage source maintains a constant output voltage, regardless of the value of R L . R V 10 V lt R L 10 V V R L = 10 V o lt s The ideal model can be called the first approximation. A real voltage source has a series resistance a series resistance . R L 10 V R S V R L < 10 Volts L 10 V R L This model is called the th d i ti th e secon d approx i ma ti on. When R L is equal to or greater than 100 times R S ,areal When R L is equal to or greater than 100 times R S , a real voltage source is stiff and the first approximation can be used. An ideal current source maintains a constant An ideal current source maintains a constant output current, regardless of the value of R L . R I 1A R L 1 A I R L = 1 A mpere The ideal model can be called the first approximation. A real current source has a shunt resistance a shunt resistance . R I 1A R R L 1 A I R L < 1 A mpere R S This model is called the th d i ti th e secon d approx i ma ti on. When R S is equal to or greater than 100 times R L ,areal When R S is equal to or greater than 100 times R L , a real current source is stiff and the first approximation can be used. Thevenin’s theorem can be used to replace any linear circuit with an equivalent voltage source linear circuit with an equivalent voltage source called V TH and an equivalent resistance called R TH . 6 k Ω 4 k Ω 3 k Ω R L 72 V V TH R TH TH TH Remove the load. Calculate or measure V across the open terminals Remove the source. Calculate or measure R TH . Calculate or measure V TH across the open terminals . Remove the source. Calculate or measure R TH . When working with actual circuits, please remember this g uideline: The input impedance of a voltmeter should be at least 100 times greater than the Thevenin resistance to avoid loading error. DMMs are usually not a problem since they DMMs are usually not a problem since they typically have an impedance of 10 MΩ. 6k Ω 6 k Ω 4 k Ω 3 kΩ R L 72 V The original circuit circuit 6 kΩ (R TH ) R The Thevenin R L 24 V (V TH ) equivalent circuit