Lecture 241 Circuits with Dependent Sources Strategy: Apply KVL and KCL, treating dependent source(s) as independent sources. Determine the relationship between dependent source values and controlling parameters. Solve equations for unknowns.
Lecture 242 Example: Inverting Amplifier The following circuit is a (simplified) model for an inverting amplifier created from an operational amplifier (op-amp). It is an example of negative feedback.
Lecture 243 Inverting Amplifier 1k + - 4k 10k VfVf V s =100V f 10V I
Lecture 244 Inverting Amplifier Apply KVL around loop: -10V + 1k I + 4k I + 10K I V f = 0 Get V f in terms of I: V f + 4k I + 100V f = 0 V f = 4k I
Lecture 245 Inverting Amplifier Solve for I: I = 1.961mA Solve for V f : V f = V Solve for source voltage: V s = -19.4V
Lecture 246 Amplifier Gain Repeat the previous example for a gain of 1000
Lecture 247 Answer V s = V
Lecture 248 Another Amplifier 1k + - 4k 10nF VfVf V s =100V f 10V 0 I Find the output voltage V s for this circuit, assuming a frequency of =5000
Lecture 249 Find Impedances 1k + - 4k -j2k VfVf V s =100V f 10V 0 I
Lecture 2410 Another Amplifier Apply KVL around loop: -10V 0 + 1k I + 4k I - j2k I V f = 0 Get V f in terms of I: V f - j2k I V f = 0 V f = j2k I
Lecture 2411 Another Amplifier Solve for I: I = 2mA -0.2 Solve for V f : V f = 39.6mV 89.8 Solve for source voltage: V s = 3.96V 89.8
Lecture 2412 Transistor Amplifier A small-signal linear equivalent circuit for a transistor amplifier is the following: Find V 3k 6k + - V5mA 5 V
Lecture 2413 Apply KCL at the Top Node 5mA = V/6k + 5 V + V/3k 5mA = 1.67 V + 5 V V V=5mA(1.67 ) V=5V