1. (15 points) Let's revisit the idea of constructing a 6V power supply from a 15 V power supply. On the midterm, you were allowed to use only resistors. Now you may use op amps, too. Design this supply. What is the range of loads to which it will supply 6 V, within our usual 10% tolerance?
2. (15 points) In Lab 8-8, you drove a push-pull with the output of the op amp. When the feedback resistor was connected to the push-pull's output, instead of the op amp's output, the crossover distortion was pretty much cured. What did the output of the op amp do to eliminate this distortion?
3. (10 points) Also in Lab 8-8, you connected a speaker to the output of the push-pull. This is the point at which many students cooked a transistor or two. Why did this not happen until they connected the speaker?
4. (15 points) Suppose the circuit in Figure L9.10 (the active rectifier) is driven with a sine wave of amplitude 2 V (that is, 4 V peak-to-peak). Carefully sketch V in vs t. Beneath that, on the same time scale, sketch V out . Beneath that, sketch the voltage at the op amp output. Beneath that, sketch the current. What is the path of this current? Make sure that all your graphs have the times and the amplitudes clearly labeled.
5. (15 points) Describe two simple changes to the circuit of Figure L10.7, each of which would double the frequency of this sawtooth oscillator. What if you made both changes at once?
6. (10 points) In Figure L9.4, there are two elements in the feedback chain, a resistor and a capacitor. What is the function of each of them?
7. (5 points) In Figure L4.4, what is the function of the 7.5 k resistor?
8. (15 points) Consider the simple inverting amplifier in Figure L8.3, and assume it's connected to supplies of ±15 V. When the input voltage is 1 V, what is the output voltage, and what is the voltage at the inverting input? When the input voltage is 2 V, what are those voltages? Are those voltages consistent with normal op amp behavior?
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You'll have at least 24 hours to complete the final, as usual.