Power semiconductors
Why is a switching power supply more efficient than a linear power supply, which operates its transistor linearly?
- ABecause the transistor is used fully on or fully off, minimizing the time it sees voltage and current at once
- BBecause it uses no transistors
- CBecause its output voltage is always higher than its input
Show answer and explanation
Answer: A. Because the transistor is used fully on or fully off, minimizing the time it sees voltage and current at once
A transistor's loss is the product of voltage and current. In a linear supply, the transistor carries current while dropping the excess voltage, so losses are large. A switching supply alternates between on (almost zero voltage) and off (almost zero current), so losses are small and efficiency is high.
- A. Correct. It minimizes the time voltage and current are present at once.
- B. Switching supplies also use transistors, as switches.
- C. Switching supplies include both step-down and step-up types.