Turn-on and turn-off times of a thyristor For a thyristor, the relative magnitudes of turn-on time (t_on) and turn-off time (t_off) are typically:

Introduction / Context:Dynamic characteristics of thyristors matter for line-commutated converters and forced-commutated choppers/inverters. Turn-on and turn-off intervals constrain permissible firing angles, commutation margins, and achievable switching frequencies.

Given Data / Assumptions:

• Classical PNPN silicon SCRs.
• Typical microsecond-level turn-on; significantly longer recovery (turn-off) time.

Concept / Approach:

Turn-on involves carrier injection and regenerative latch-up, which is fast once gate current and anode current exceed latching thresholds. Turn-off requires removal of stored charge and recovery of junction blocking capability, which takes longer (reverse recovery + recombination). Therefore, t_off is much greater than t_on in standard thyristors, limiting their use at high switching frequencies.

Step-by-Step Solution:

Verification / Alternative check:

Datasheets list t_on often in the range of a few microseconds, while t_q (turn-off) can be tens or hundreds of microseconds for line-frequency devices.

Why Other Options Are Wrong:

(a), (b), and (d) do not reflect practical device physics; arbitrary ratios like option (e) are not general.

Common Pitfalls:

Assuming symmetry between turn-on and turn-off dynamics; overlooking that GTOs/IGCTs and modern devices have improved but still non-equal times.

Final Answer:

t_off ≫ t_on