Assertion–Reason: Inverters and choppers employ fast-switching thyristors because these devices have low turn-off time (tq). Evaluate the statements.

Introduction / Context:
High-frequency switching converters (inverters and choppers) demand devices that can turn on and, crucially, turn off rapidly to minimize switching losses and allow higher operating frequencies. Fast-switching thyristors are engineered for low reverse recovery and short turn-off times.

Given Data / Assumptions:

• Assertion (A): Inverters and choppers use fast-switching SCRs/thyristors.
• Reason (R): Fast-switching SCRs have low turn-off time tq.
• Focus is on commutation speed and loss reduction.

Concept / Approach:

Turn-off time tq determines the minimum interval after current extinction before a thyristor can block forward voltage again. Lower tq enables higher switching frequency and reduces overlap/recovery losses—key requirements in PWM inverters and dc choppers.

Step-by-Step Evaluation:

Verification / Alternative check:

Datasheets specify tq and trr (recovery) for inverter-grade SCRs; application notes tie allowable PWM frequency to tq margins.

Why Other Options Are Wrong:

• Stating R does not explain A contradicts the direct link between low tq and converter suitability.
• Any claim that A or R is wrong conflicts with standard converter design practice.

Common Pitfalls:

• Confusing di/dt ratings with tq; both matter, but tq governs maximum switching frequency.
• Overlooking that modern designs often prefer IGBTs/MOSFETs for even faster switching.

Final Answer:

Both A and R are correct and R is correct explanation of A