Power electronics safety: A thyristor (SCR) requires protection against which rapid transients during turn-on and commutation?

Introduction / Context:
Silicon Controlled Rectifiers (thyristors) are robust but vulnerable to certain electrical transients. Designers must limit both the rate of rise of current (di/dt) and the rate of rise of voltage (dv/dt) to prevent localized damage, nuisance triggering, or loss of control.

Given Data / Assumptions:

• Thyristor conduction begins in a small junction area and spreads across the device.
• Turn-on and commutation periods are critical for stress.
• Protection networks (snubbers, series inductance) are common.

Concept / Approach:

Excess di/dt during turn-on can cause current crowding, overheating a small silicon area before conduction spreads fully. Excess dv/dt can charge junction capacitances and inadvertently trigger the device (false turn-on). Thus, both transients must be limited via series inductors (for di/dt) and RC snubbers or controlled gating (for dv/dt).

Step-by-Step Solution:

Verification / Alternative check:

Manufacturer datasheets specify maximum di/dt and dv/dt ratings and recommend protective components in typical application circuits.

Why Other Options Are Wrong:

• “Only di/dt” or “only dv/dt” ignores half the risk profile.
• “Either one” is incomplete; robust design handles both.

Common Pitfalls:

Underestimating dv/dt-induced false triggering, especially in inductive environments and high dV nodes without proper snubbing.

Final Answer:

Both high di/dt and high dv/dt