Power Supply Interview Q&A: Top 10 Questions

This questionnaire will help you pass job interviews for various Power Supply skill-based positions, and will also be useful during vivas for engineering students.

Power Supply Questions and Answers

Question 1: What is a power supply, and what are its main functions?

Answer 1: A power supply is an electronic device that provides electrical energy to an electrical load. Its main functions are to convert electrical power from one form to another (e.g., AC to DC), regulate the output voltage or current, protect against overvoltage, and ensure a stable and reliable power source for electronic devices.

Question 2: Explain the difference between a linear power supply and a switching power supply.

Answer 2: A linear power supply regulates the output voltage by dissipating excess power as heat through a series of transistors or resistors. This provides a smooth and noise-free DC output, but with lower efficiency. A switching power supply, on the other hand, converts AC to DC by switching the input power on and off rapidly. This uses less energy and provides higher efficiency, but with more complex circuitry and the potential for increased noise.

Question 3: What is the purpose of a transformer in a power supply?

Answer 3: A transformer in a power supply is used to step up or step down the input AC voltage to the desired level before rectification and regulation. It also provides electrical isolation between the input and output, ensuring safety and protecting the circuit from potential surges or faults in the input power.

Question 4: Describe the role of a rectifier in a power supply.

Answer 4: A rectifier converts alternating current (AC) to direct current (DC) by allowing current to flow in only one direction. In a power supply, the rectifier is responsible for converting the AC voltage from the transformer into a pulsating DC voltage, which is then filtered and regulated to produce a steady DC output.

Question 5: What is voltage regulation, and why is it important in a power supply?

Answer 5: Voltage regulation is the process of maintaining a constant output voltage regardless of changes in input voltage or load conditions. It is crucial in a power supply to ensure that electronic devices receive a stable and consistent voltage, preventing damage or malfunction due to voltage fluctuations.

Question 6: What is the difference between a regulated and an unregulated power supply?

Answer 6: A regulated power supply maintains a constant output voltage even when there are changes in the input voltage or load. It typically uses a voltage regulator circuit. An unregulated power supply, however, does not have this capability, and its output voltage may vary with changes in input voltage or load, making it less suitable for sensitive electronic devices.

Question 7: Explain the concept of ripple voltage in a power supply.

Answer 7: Ripple voltage is the residual periodic variation of the DC output voltage within a power supply, caused by incomplete suppression of the alternating waveform after rectification. Ripple voltage is undesirable because it can introduce noise into the circuit, potentially affecting the performance of sensitive electronic components. It is typically reduced using filtering components like capacitors and inductors.

Question 8: What is the purpose of a filter capacitor in a power supply?

Answer 8: A filter capacitor in a power supply is used to smooth out the pulsating DC voltage from the rectifier, reducing the ripple voltage. It stores and releases energy to fill in the gaps of the rectified waveform, providing a more stable DC output. The larger the capacitance, the better the filtering effect.

Question 9: What is the significance of power supply efficiency, and how is it calculated?

Answer 9: Power supply efficiency is a measure of how well the power supply converts input power into usable output power, expressed as a percentage. It is calculated using the formula:

Higher efficiency means less energy is wasted as heat, resulting in lower operating costs and reduced thermal management requirements.

Question 10: What are some common protection features in power supplies, and why are they important?

Answer 10: Common protection features in power supplies include overvoltage protection (OVP), overcurrent protection (OCP), short-circuit protection (SCP), and thermal shutdown. These features are important because they prevent damage to the power supply and connected devices by shutting down or limiting the output when abnormal conditions are detected, ensuring safe and reliable operation.