HAM Practical Electronics Circuits 2 — Questions and Answers
Question 1: What is the primary purpose of a bypass capacitor placed near an IC power supply pin?
- To increase the supply voltage
- To filter high-frequency noise from the supply rail (Correct answer)
- To slow down the rise time of digital signals
- To store energy for transmit bursts
Correct answer: To filter high-frequency noise from the supply rail
Bypass capacitors filter high-frequency noise on the power supply rail, preventing it from coupling into sensitive IC circuitry.
Question 2: Which configuration of a bipolar junction transistor (BJT) provides both voltage and current gain?
- Common base
- Common collector
- Common emitter (Correct answer)
- Emitter follower
Correct answer: Common emitter
The common-emitter configuration provides both voltage gain and current gain, making it the most widely used amplifier topology.
Question 3: In a Class AB amplifier, what problem does the small forward bias on the output transistors solve?
- Voltage clipping at high power
- Crossover distortion present in Class B amplifiers (Correct answer)
- Thermal runaway in Class A amplifiers
- Impedance mismatch at the load
Correct answer: Crossover distortion present in Class B amplifiers
A small forward bias keeps the output transistors just at the edge of conduction, eliminating the dead-zone crossover distortion of Class B.
Question 4: What does the slew rate of an operational amplifier specify?
- The maximum DC gain before saturation
- The input offset voltage drift with temperature
- The maximum rate of change of the output voltage in V/µs (Correct answer)
- The common-mode rejection ratio at high frequencies
Correct answer: The maximum rate of change of the output voltage in V/µs
Slew rate is the maximum speed at which an op-amp's output voltage can change, expressed in volts per microsecond.
Question 5: A Zener diode is used in reverse breakdown primarily to:
- Rectify an AC signal
- Provide a stable reference voltage (Correct answer)
- Amplify weak RF signals
- Block DC while passing AC
Correct answer: Provide a stable reference voltage
Zener diodes are designed to operate in reverse breakdown, maintaining a nearly constant voltage across their terminals for regulation or reference use.
Question 6: What type of feedback is used in a voltage-regulator op-amp circuit where the output is sampled and returned to the inverting input?
- Positive voltage feedback
- Negative voltage feedback (Correct answer)
- Current-series feedback
- Positive current feedback
Correct answer: Negative voltage feedback
Sampling the output voltage and feeding it back to the inverting input is classic negative voltage feedback, which stabilizes the output.
Question 7: Which component in a switching power supply controls the duty cycle to regulate output voltage?
- The output filter inductor
- The rectifier diode
- The PWM controller IC (Correct answer)
- The input capacitor bank
Correct answer: The PWM controller IC
The PWM (pulse-width modulation) controller IC compares the output voltage to a reference and adjusts the duty cycle of the switching transistor accordingly.
HAM Practical Electronics Circuits 2
What is the primary purpose of a bypass capacitor placed near an IC power supply pin?