Power control devices — DC vs. AC suitability: “The triac provides better DC power control than the SCR.” Assess this statement considering device physics and typical applications.

Introduction / Context:
Triacs and silicon-controlled rectifiers (SCRs, or thyristors) are common in power control. Understanding which device fits DC control versus AC control prevents serious design errors. The prompt claims triacs are better for DC control, which runs counter to standard practice.

Given Data / Assumptions:

• Triac: bidirectional device, primarily intended for AC phase control (conducts both polarities).
• SCR: unidirectional device, commonly used in controlled rectifiers and DC switching.
• Turn-off (commutation) mechanism differs between AC and DC systems.

Concept / Approach:
Triacs rely on current falling below a holding value to turn off. In AC circuits, the line current naturally crosses zero every half-cycle, providing natural commutation. In DC circuits, there is no natural current zero; once triggered, a triac may remain latched until supply removal or forced commutation—making it poor for straightforward DC control. SCRs, by contrast, are inherently suited to DC power control in chopper/controlled rectifier topologies with appropriate commutation schemes, and they offer robust current handling in one direction.

Step-by-Step Solution:

Verification / Alternative check:
Application notes show triacs dominating light dimmers and AC motor speed controls (single-phase), whereas SCRs appear in DC supplies, HV DC links, field excitation of machines, and rectifier bridges.

Why Other Options Are Wrong:

• Correct: Contradicts established application domains.
• “Valid only below 12 V DC” / “Valid with freewheel diode”: Neither fixes the latching/commutation issue.
• “Undetermined without heat-sink data”: Thermal design matters but does not change suitability.

Common Pitfalls:
Assuming any bidirectional device is superior; forgetting that device turn-off physics dictates application fit.

Final Answer:
Incorrect.