CET Power Supply Design & Repair 3

Question 1

What is the purpose of a snubber circuit across a switching transistor in an SMPS?

Accepted Answer

Suppress voltage spikes caused by transformer leakage inductance

Answer

Increase switching frequency

Answer

Boost output current capacity

Answer

Provide soft-start capability

Question 2

Which measurement tool is best suited for evaluating the ESR of electrolytic capacitors in a power supply?

Accepted Answer

ESR meter or LCR meter with ESR function

Answer

Standard DMM on capacitance range

Answer

Oscilloscope only

Answer

Simple ohmmeter

Question 3

A 78xx series three-terminal regulator requires a minimum input-to-output voltage differential to regulate properly. This is called the:

Accepted Answer

Dropout voltage

Answer

Ripple rejection ratio

Answer

Line regulation

Answer

Load regulation

Question 4

When testing a power supply under load and the output voltage drops significantly, which parameter is being evaluated?

Accepted Answer

Load regulation

Answer

Line regulation

Answer

Ripple rejection

Answer

Transient response

Question 5

What is the primary safety hazard when working on the primary side of a plugged-in switching power supply?

Accepted Answer

High-voltage AC/DC present even when power switch is off

Answer

Low-voltage DC shock

Answer

RF interference

Answer

Overheating of output inductors

Question 6

In a flyback converter, energy is stored in the transformer core during which switch state?

Accepted Answer

When the switch is ON

Answer

When the switch is OFF

Answer

During the blanking time

Answer

Only at startup

Question 7

A power supply produces a loud high-pitched whine under load. What is the most likely cause?

Accepted Answer

Loose or saturating transformer/inductor core

Answer

Faulty output rectifier

Answer

Open input fuse

Answer

Failed PWM IC