Electronic principles - Chapter 1

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Nội dung Text: Electronic principles - Chapter 1

MALVINO Electronic PRINCIPLES SIXTH EDITION
Introduction Chapter 1
Three kinds of formulas The definition: Invented for a new concept Q {defines what capacitance is} C= V {does not require verification} The law: Summarizes a relationship that exists in nature Q1Q2 f=K {verified by experiment} d 2 The derivation: Obtained by manipulating other formulas using mathematics Q = CV
An ideal voltage source maintains a constant output voltage, regardless of the value of RL. RL VR = 10 Volts 10 V L The ideal model can be called the first approximation.
A real voltage source has a series resistance. RS VR < 10 Volts RL 10 V L This model is called the the second approximation. When RL is equal to or greater than 100 times RS, a real voltage source is stiff and the first approximation can be used.
An ideal current source maintains a constant output current, regardless of the value of RL. RL IR = 1 Ampere 1A L The ideal model can be called the first approximation.
A real current source has a shunt resistance. RL RS IR < 1 Ampere 1A L This model is called the the second approximation. When RS is equal to or greater than 100 times RL, 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 called VTH and an equivalent resistance called RTH. 6 kΩ 4 kΩ RL V 72 V 3 kΩ R THTH Calculate or CalculateVTHthe load. RTH. terminals. Remove asource. measure or measure open Remove the cross the
When working with actual circuits, please remember this guideline: 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 typically have an impedance of 10 MΩ .
6 kΩ 4 kΩ The original RL 72 V 3 kΩ circuit 6 kΩ (RTH) The Thevenin RL 24 V (VTH) equivalent circuit
Norton’s theorem can be used to replace any linear circuit with an equivalent current source called IN and an equivalent resistance called RN. 6 kΩ 4 kΩ RL I 72 V 3 kΩ RNN RN is the same as RTH. I . Short the load to find N
6 kΩ 4 kΩ The original RL 72 V 3 kΩ circuit The Norton RL 6 kΩ (RN) 4 mA (IN) equivalent circuit
6 kΩ (RTH) A Thevenin RL 24 V (VTH) equivalent circuit VTH RN = RTH IN = RTH The Norton RL 6 kΩ (RN) 4 mA (IN) dual
Troubleshooting • A solder bridge between two lines effectively shorts them together. • A cold solder joint is effectively an open circuit. • An intermittent trouble is one that appears and disappears (could be a cold solder joint or a loose connection).
An open device • The current through it is zero. • The voltage across it is unknown. • V = zero x infinity {indeterminate}
A shorted device • The voltage across it is zero. • The current through it is unknown. • I = 0/0 {indeterminate}
A troubleshooting example: Do the two 10 Ω resistors form a stiff voltage divider? 10 Ω 100 kΩ 100 kΩ 12 V 10 Ω Why?
A troubleshooting example: What are the expected voltages in this circuit? 10 Ω 100 kΩ 100 kΩ 12 V 10 Ω
A troubleshooting example: What are some causes for this voltage being too high? 10 Ω 100 kΩ V 100 kΩ 12 V 10 Ω
A troubleshooting example: What are some causes for this voltage being too low? 10 Ω 100 kΩ V 100 kΩ 12 V 10 Ω