Practice Test Geeks(CET) Certified Electronics Technician Practice Test
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CET Power Supplies and Electrical Safety Flashcards

6 cards from real CET practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 6 CET Power Supplies and Electrical Safety flashcards as text

  1. In what frequency range do typical switch-mode power supplies (SMPS) operate their switching transistors?

    Answer: 20 kHz to several hundred kHz

    SMPS circuits typically switch at 20 kHz–500 kHz, allowing much smaller transformer and filter components compared to line-frequency designs.

  2. What is the primary advantage of a switching power supply over a linear regulator for the same output power?

    Answer: Much higher efficiency (often 80–95%) because the switching transistor is either on or off

    Switching regulators achieve high efficiency because the transistor dissipates very little power while fully on or fully off, unlike linear regulators.

  3. What is the purpose of Power Factor Correction (PFC) circuitry in an AC-DC power supply?

    Answer: Make the input current waveform sinusoidal and in phase with the voltage to reduce reactive power and harmonic distortion

    PFC shapes the input current to follow the input voltage waveform, bringing power factor close to unity and reducing harmonic distortion on the supply line.

  4. In a buck (step-down) DC-DC converter, what primarily determines the output voltage?

    Answer: The duty cycle of the switching transistor

    In a buck converter, Vout = D × Vin, where D is the duty cycle (on-time/period), so the output voltage is controlled by adjusting duty cycle.

  5. What is the primary purpose of an isolation transformer used with electronic test equipment?

    Answer: Prevent direct electrical connection to the AC mains so neither output terminal is referenced to earth ground

    An isolation transformer breaks the earth-ground reference, making it safer to work on equipment connected to the mains without risk of a ground-referenced shock.

  6. What is the function of a flyback diode (freewheeling diode) connected across an inductive load in a switching power supply?

    Answer: Provide a current path for inductor energy when the switch opens, preventing large voltage spikes

    When the switch opens, inductor current cannot stop instantly; the flyback diode conducts this current, preventing a destructive voltage spike across the transistor.