ISCET Power Supply Circuits and Voltage Regulation

Question 1

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

Accepted Answer

To smooth the pulsating DC output by reducing ripple

Answer

A filter capacitor charges to the peak voltage and slowly discharges between peaks, reducing the ripple and smoothing the pulsating DC into a more stable output.

Question 2

A half-wave rectifier is connected to a 120V RMS transformer secondary. What is the approximate average DC output voltage (ignoring diode drop)?

Accepted Answer

54V

Answer

For a half-wave rectifier, Vavg = 0.318 × Vpeak = 0.318 × (120 × 1.414) ≈ 0.318 × 169.7 ≈ 54V.

Question 3

In a full-wave bridge rectifier, how many diodes conduct simultaneously during each half-cycle of the AC input?

Accepted Answer

Two

Answer

In a bridge rectifier, current flows through two diodes in series during each half-cycle — one on the top rail and one on the bottom rail.

Question 4

The ripple factor (r) of a power supply filter is best described as:

Accepted Answer

The ratio of RMS ripple voltage to average DC output voltage

Answer

Ripple factor r = Vrms(ripple) / Vdc, and a lower value indicates a better-filtered, more stable DC output.

Question 5

A 7812 three-terminal linear voltage regulator produces which regulated output voltage?

Accepted Answer

12V

Answer

The 78XX series regulators output a voltage equal to the last two digits; the 7812 outputs a fixed +12V regulated output.

(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