CET CET Power Supplies and Electrical Safety 1

Question 1

What is the primary purpose of a filter capacitor placed after the rectifier in a DC power supply?

Accepted Answer

Reduce output ripple by storing charge between rectifier pulses

Answer

The filter capacitor charges to the peak voltage and slowly discharges into the load between pulses, smoothing the pulsating DC.

Question 2

At what frequency does the ripple voltage appear in a full-wave bridge rectifier powered by a 60 Hz AC supply?

Accepted Answer

120 Hz

Answer

A full-wave rectifier produces two pulses per AC cycle, so ripple frequency equals twice the supply frequency: 2 × 60 = 120 Hz.

Question 3

Which type of voltage regulator dissipates the difference between input and output voltage as heat?

Accepted Answer

Linear regulator

Answer

Linear regulators pass current through a series pass transistor that drops the excess voltage as heat, making them less efficient than switchers.

Question 4

How does a zener diode function as a voltage regulator in a shunt regulator circuit?

Accepted Answer

It maintains a nearly constant voltage across it by varying the current through it within its breakdown region

Answer

Operating in reverse breakdown, the zener holds a fixed voltage across itself while absorbing excess current, keeping output voltage stable.

Question 5

In a power supply, what does a crowbar circuit do?

Accepted Answer

Immediately short the output through a thyristor (SCR) if voltage exceeds a safe threshold, blowing the fuse

Answer

A crowbar circuit fires an SCR to short the output when overvoltage is detected, causing the fuse to blow and protecting downstream equipment.

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