In-Class Exercises for Lab 2: Input and Output Impedance

Transcription

1 In-Class Exercises for Lab 2: Input and Output Impedance. What is the output resistance of the output device below? Suppose that you want to select an input device with which to measure the voltage produced by this output device. What input resistance should the input device have? 0 V 2 Ω 2. If one D-cell battery has an output resistance of.5ω, what are the output resistance and output voltage of three D-cell batteries in series? In parallel? Hint: Draw the equivalent circuits. 3. We want to get the most light possible out of a light bulb and three magic.5 V batteries with no internal resistance. If the bulb has a resistance of 0.3Ω, which battery configuration, series or parallel, will result in the most current, and therefore, the most light? Recall that light output is roughly proportional to the power dissipated. 4. Find the light bulb resistance that maximizes the light output, assuming one non-ideal D-cell battery with an internal resistance of R i =.5Ω. Hint: Compute the power (P ) dissipated by the bulb as a function of the bulb resistance (R b ), set the derivative of P with respect to R b equal to zero, and solve for R b.

2 In-Class Exercises for Lab 3: AC Measurements. Given a sinusoidal -khz signal that oscillates between 5 V and 5V, what are the peak-to-peak voltage, the rms voltage, the amplitude, and the dc offset of the signal? 2. Let a 5-V peak-to-peak signal with no dc offset be the input to a voltage divider constructed from two -kω resistors. Sketch four periods of the input and expected output signals on the same graph, being careful to get the relative amplitudes right. 3. A signal generator is set up to generate a -V peak-to-peak sine wave. A 4-Ω speaker is connected to the 50-Ω output of the signal generator. What peak-to-peak voltage is actually applied to the speaker? How much power is dissipated by the speaker?

3 In-Class Exercises for Lab 4: RC Circuits and Filters. What resistance in series with a 00 μf capacitor will yield a second time constant? 2. Suppose that we send a 0 V peak-to-peak -khz square wave with zero offset into the input of the circuit below. Calculate the RC time constant and use the expression for exponential decay to determine the expected maximum peak-to-peak voltage at the output. Sketch several periods of the input signal together with the expected output signal on the same graph, taking care to get the relative amplitudes right. kω μf 3. You have an audio amplifier, and you wish to amplify signals with frequencies of 2000 Hz or greater. Unfortunately, there is a lot of unwanted 60-Hz noise on your microphone input. Design a filter circuit that will attenuate the 60-Hz pickup without affecting the desired frequencies too much. Note that filter circuits usually use capacitors of less than about μf and resistors of at least a few kω. Drawyourcircuit below and label the values of all components. Also find the ratio / for both 60 Hz and 2000 Hz for your design. 4. You are looking at a signal from a plasma discharge experiment that is in the frequency range of 50 khz to 5 MHz. Unfortunately, the discharge itself produces lots of highfrequency noise at frequencies well above the frequency range of interest for the signal. Design a filter that will leave the desired signal intact but attenuate the nasty veryhigh-frequency stuff.

4 In-Class Exercises for Lab 5: Diodes and Rectification. For the diode circuit below, =(2V)sin(ωt). Sketch as a function of t. 2. The circuit below shows a configuration of diodes called a diode bridge. Consider the path of current through the bridge circuit when point A is at a higher voltage than point B. Draw arrows in the direction that current flows through the diodes and label them with a. Now consider what happens when point B is at a higher voltage than point A. Label these currents with a 2. What is the sign of the voltage in both of these cases? Draw a qualitative sketch of the output voltage as a function of t if the voltage on the output of the transformer is as shown (V AB = V B V A ). A 0 VAC B R L V AB t 3. Make an estimate (an upper bound, actually) for the amount of ripple on a 00 μf capacitor in a power supply that has 0 ma of current drawn from it. Remember that thetimebetweenpeaksis 20 second.

5 In-Class Exercises for Lab 6: Transistors and MOSFETs. In the transistor switching circuit below, assume that R is 00 kω. How much current goes through the resistor when the switch is turned on, and what will the light bulb do? Reconsider these questions for R =0kΩand R =kω. 0V R b c e 00 Ω when lit 2. The following circuit is an emitter follower. =(3V)(V)sin(ωt). Sketch as a function of t. What happens to if a 500 Ω load is attached to the follower output? 0 V k 3. When an output device is used to directly drive a load resistor R L, the input resistance of the load is simply equal to R L. However, when the load is incorporated into a FET switch as shown below, the input resistance is increased. Estimate the effective input resistance of this new configuration. V CC R L

6 In-Class Exercises for Lab 7: Operational Amplifiers. Calculate the gain / for the circuit shown below. 0 kω kω 2. Calculate the gain / for the circuit shown below. kω 0 kω 3. Calculate the gain / for the circuit shown below. Additional exercises on the next page

7 In-Class Exercises for Lab 8: Comparators. Sketch the output for the op-amp circuit below when the input is a sine wave of amplitude V CC. Note the limits on the voltage divider. V CC k 2k -V CC 2. (a) When no feedback resistor is present in the circuit shown below, what nominal reference voltage V ref is produced by the voltage divider on the left? (b) When the feedback resistor is present, alters the value of V ref. When the rises above V ref, the output swings to ground causing V ref to change to what value? (c) Because this op-amp has an open collector output, it requires a 00-Ω pull-up resistor on the output. When drops below V ref, the output swings up to 5 V causing V ref to change to what value (ignore the small contribution of the pull-up resistance)? 5 V 5V 2k 00 V ref k 0 k