Advanced Qualification · A-004 Power supplies · A-004-004-001
In a series-regulated power supply, the power dissipation of the pass transistor is:
- A directly proportional to the load current and the input/output voltage differential
- B the inverse of the load current and the input/output voltage differential
- C dependent upon the peak inverse voltage appearing across the Zener diode
- D indirectly 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: rectifiers, filtering, regulation, switching supplies and their failure modes.