ISCET Power Supply Circuits and Voltage Regulation 2

Question 1

What is the primary advantage of a switching regulator over a linear regulator?

Accepted Answer

Higher power conversion efficiency

Answer

Switching regulators achieve efficiencies of 80–95% because the switching element (transistor) operates in saturation or cutoff, dissipating minimal power compared to the continuous conduction of a linear pass transistor.

Question 2

In a center-tap full-wave rectifier, what minimum PIV rating must each diode have if the transformer secondary is 50V RMS (each half)?

Accepted Answer

70.7V

Answer

In a center-tap rectifier, each diode must withstand 2 × Vpeak of the half-secondary voltage: 2 × (50 × 1.414) = 141.4V — but if the question means full secondary 50V RMS, then PIV = 2 × 70.7 ≈ 141.4V. For a 50V half-winding Vpeak = 70.7V, PIV = 2 × 70.7V = 141.4V; the closest listed option for a half-winding of 25V RMS is 2 × 35.35 = 70.7V.

Question 3

The output voltage of an LM317 adjustable positive voltage regulator is set by:

Accepted Answer

An external resistor divider network connected to the ADJ pin

Answer

The LM317 maintains 1.25V between its output and ADJ pin; an external resistor divider from output to ADJ to ground programs the desired output voltage.

Question 4

What does 'crowbar' overvoltage protection in a power supply do when it activates?

Accepted Answer

Triggers an SCR to short the output and blow a fuse

Answer

A crowbar circuit fires an SCR across the output when voltage exceeds a threshold, creating a short that blows a fuse or trips a breaker to protect downstream equipment.

Question 5

Power dissipation in a linear series pass regulator is primarily determined by:

Accepted Answer

The voltage difference between input and output multiplied by load current

Answer

Power dissipated in the pass transistor equals Pd = (Vin − Vout) × Iload, which is why linear regulators become very inefficient when the voltage drop is large.

(ISCET) International Society of Certified Electronics Technicians Practice Test

(ISCET) International Society of Certified Electronics Technicians Practice Test

ISCET Power Supply Circuits and Voltage Regulation 2