Lecture Notes for Analog Electronics - The Electronic Universe ...

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1.4 Thevenin’s Theorem Vin Figure 3: A voltage divider. Thevenin’s theorem states that any circuit consisting of resistors and EMFs has an equivalent circuit consisting of a single voltage source VTH in series with a single resistor RTH. The concept of “load” is useful at this point. Consider a partial circuit with two output points held at potential difference Vout which are not connected to anything. A resistor RL placed across the output will complete the circuit, allowing current to flow through RL. The resistor RL is often said to be the “load” for the circuit. A load connected to the output of our voltage divider circuit is shown in Fig. 4 The prescription for finding the Thevenin equivalent quantities VTH and RTH is as follows: • For an “open circuit” (RL →∞), then VTH = Vout . • For a “short circuit” (RL → 0), then RTH = VTH/Ishort. An example of this using the voltage divider circuit follows. We wish to find the Thevenin equivalent circuit for the voltage divider. Vin R 1 R 1 R 2 Vout R 2 Vout R L Figure 4: Adding a “load” resistor RL. 3
The goal is to deduce VTH and RTH to yield the equivalent circuit shown in Fig. 5. V TH R TH Figure 5: The Thevenin equivalent circuit. To get VTH we are supposed to evaluate Vout when RL is not connected. This is just our voltage divider result: � � R2 VTH = Vin R1 + R2 Now, the short circuit gives, by Ohm’s Law, Vin = IshortR1. Solving for Ishort and combining with the VTH result gives RTH = VTH/Ishort = R1R2 R1 + R2 Note that this is the equivalent parallel resistance of R1 and R2. This concept turns out to be very useful, especially when different circuits are connected together, and is very closely related to the concepts of input and output impedance (or resistance), as we shall see. 4 R L
Page 1 and 2: Lecture Notes for Analog Electronic
Page 3: 1.2.1 Resistors in series I3 I1 I2
Page 7 and 8: Thus, we should try to keep the rat
Page 9 and 10: Note that in this case Vin can be a
Page 11 and 12: Thus, we have an expression of the
Page 13 and 14: The decibel scale works as follows:
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Page 17 and 18: Vin L C Figure 12: A RLC circuit. S
Page 19 and 20: A diode is fabricated from a pn jun
Page 21 and 22: Class Notes 5 5 Transistors and Tra
Page 23 and 24: 5.1.2 Transistor Switch and Saturat
Page 25 and 26: Class Notes 6 Following our discuss
Page 27 and 28: V in C R 1 R 2 V cc R C R E V out F
Page 29 and 30: In 1 and similarly for output 2 R C
Page 31 and 32: Class Notes 8 5.8 More on Transisto
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Page 35 and 36: Hence, variations in β are attenua
Page 37 and 38: 2. The inputs draw no current. ( Th
Page 39 and 40: Perhaps the best way to beat these
Page 41 and 42: 6.6.1 Gain IN C - + R OUT Figure 34
Page 43 and 44: Therefore, the efect of the closed
Page 45 and 46: 7 Comparator Circuits 7.1 Simple Co
Page 47 and 48: V h Vl +5 v in V out Figure 40: Exa
Page 49 and 50: 8 Radio Basics Class Notes 11 In th
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