Power/trigger devices: Match each device with a characteristic application or control property. List I List II A. GTO 1. Widely used as switches in digital computers B. UJT 2. Used for freewheeling (commutation) paths C. Power diode 3. Can be turned off by a negative gate signal D. MOSFET 4. Used in generating triggering pulses (relaxation oscillator)

Introduction / Context:
Power electronics integrates devices with distinct control behaviors. Recognizing their hallmark uses is essential for converter and trigger design.

Given Data / Assumptions:

• GTO = Gate Turn-Off thyristor.
• UJT = Unijunction transistor.
• Power diode used in rectifiers and freewheeling paths.
• MOSFET commonly used as the basic switch in digital logic.

Concept / Approach:

Map each device’s well-known control trait: GTO’s gate-off capability, UJT’s relaxation oscillation for triggering, power diode’s freewheeling role, and MOSFET’s ubiquity in digital switching.

Step-by-Step Solution:

Verification / Alternative check:

Converter schematics show freewheeling diodes across inductors; UJT timers in classic firing circuits; GTO datasheets specify gate-off conditions; MOSFETs populate logic ICs and CPUs (CMOS).

Why Other Options Are Wrong:

• Swapping GTO with diode ignores their fundamentally different control.
• Assigning “freewheeling” to MOSFETs mislabels the role; the intrinsic body diode is not the primary freewheel device in all designs.

Common Pitfalls:

Assuming SCRs can all be turned off by gate—only GTOs have gate turn-off capability; standard SCRs require current fall below holding current or forced commutation.

Final Answer:

A-3, B-4, C-2, D-1