Power Supply Design & Repair Flashcards

Which component in a linear power supply is primarily responsible for reducing AC input voltage before rectification?

Answer: Power transformer

The power transformer steps down the AC mains voltage to a lower AC level suitable for the rectifier stage.

In a switching power supply, what is the primary function of the PWM (Pulse Width Modulation) controller IC?

Answer: Regulate output voltage by adjusting switch duty cycle

The PWM controller IC varies the duty cycle of the switching transistor to maintain a regulated DC output voltage.

A technician measures excessive ripple on a power supply output. Which component is most likely failing?

Answer: Output filter capacitor

Electrolytic output filter capacitors degrade over time and their increased ESR leads to excessive output ripple voltage.

What does the term 'crowbar circuit' refer to in power supply design?

Answer: An overvoltage protection circuit that shorts the output

A crowbar circuit places a short (via SCR) across the output when overvoltage is detected, blowing the fuse and protecting downstream loads.

In a full-wave bridge rectifier with a 24 V AC RMS input, approximately what is the peak DC voltage before filtering?

Answer: 33.9 V

Peak voltage equals RMS × √2, so 24 V × 1.414 ≈ 33.9 V; two diode drops reduce it slightly in practice.

Which topology is most commonly used in ATX computer power supplies due to its efficiency at high power levels?

Answer: Forward or half-bridge switching converter

ATX power supplies use forward or half-bridge switching topologies because they achieve high efficiency (>80%) at power levels of 200 W and above.

A power supply's output voltage is too high and does not respond to the trim pot adjustment. Which section should the technician inspect first?

Answer: Feedback/error amplifier network

The feedback/error amplifier network (including the voltage divider and reference) controls output regulation, and a fault there will cause uncontrolled output voltage.