Advanced Qualification · A-004 Power supplies · A-004-004-001
In a series-regulated power supply, the power dissipation of the pass transistor is:
- Adirectly proportional to the load current and the input/output voltage differential
- Bthe inverse of the load current and the input/output voltage differential
- Cdependent upon the peak inverse voltage appearing across the Zener diode
- Dindirectly proportional to the load voltage and the input/output voltage differential
Correct answer: A — directly proportional to the load current and the input/output voltage differential. From the official ISED question bank, verified word for word.
Why
In a series-regulated supply, the pass transistor acts like a variable resistor that drops the extra voltage between the input and output. The full explanation — and one for every question — is in Pro.
Practise this section
Power supplies is section A-004 of the Advanced exam: Power supplies: rectifiers, filtering, regulation, switching supplies and their failure modes.
Drill A-004 — free, no account