Power Supply Design & Repair Flashcards
7 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 7 Power Supply Design & Repair flashcards as text
In power supply design, what does 'line regulation' specify?
Answer: Output voltage change with varying AC input voltage
Line regulation measures how much the output voltage changes when the AC input (line) voltage varies across its specified range.
A power supply's output drops to zero when a certain load is connected, then recovers when the load is removed. This behavior indicates:
Answer: Overcurrent protection (OCP) or foldback current limiting is tripping
Overcurrent or foldback protection shuts down or reduces output when load current exceeds the set limit, recovering when the overload is removed.
What is the advantage of a synchronous rectifier over a standard Schottky diode in a low-voltage SMPS output?
Answer: Lower forward voltage drop, reducing conduction losses and improving efficiency
A synchronous MOSFET rectifier has an effective forward drop of only millivolts (Rds_on × I) versus 0.3–0.5 V for a Schottky, significantly improving efficiency at high currents.
When measuring transformer secondary winding continuity with an ohmmeter, a technician reads infinite resistance. This indicates:
Answer: Open winding — likely a blown fuse link or broken wire
An infinite resistance reading on a winding indicates a break in the wire, often an internal fuse link that opens under fault conditions.
Which switching frequency range is most commonly used in modern SMPS designs as a balance between component size and switching losses?
Answer: 50–500 kHz
Most SMPS designs operate between 50 kHz and 500 kHz, where transformer and capacitor sizes are manageable and switching losses are not yet dominant.
A power supply exhibits good voltage regulation at DC but poor rejection of AC line noise. Which component is most likely inadequate?
Answer: Input EMI/line filter and X/Y capacitors
The input EMI filter (common-mode chokes and X/Y capacitors) is responsible for attenuating AC line noise before it reaches the rectifier and propagates to the output.
What is the purpose of a bleeder resistor connected across the output of a power supply filter capacitor?
Answer: Discharge the filter capacitor quickly when power is removed for safety
A bleeder resistor provides a discharge path for the filter capacitor so that dangerous voltages do not remain on the output after the supply is switched off.