Gate pulse width in a single-phase full-wave AC regulator For a single-phase full-wave regulator feeding an R–L load, are short gate pulses suitable for reliable control?

Introduction / Context:
AC voltage controllers (AC regulators) use phase control of thyristors to vary RMS output. With inductive loads, current and voltage are out of phase, which affects latching and holding of SCRs. This question concerns the adequacy of short gate pulses when driving an R–L load.

Given Data / Assumptions:

• Single-phase full-wave regulator (antiparallel SCRs).
• Load has significant inductance.
• Gate pulses can be short or of adequate width (e.g., train or long pulses).

Concept / Approach:

For inductive loads, at the instant of triggering, the anode current may lag and may not immediately exceed the SCR latching current if the gate pulse is too short. A long gate pulse (or multiple pulses) ensures the device turns on firmly once the load current reaches latching/holding levels despite phase lag and source impedance. Therefore, short single pulses are generally unsuitable.

Step-by-Step Solution:

Verification / Alternative check:

Oscilloscope traces in application notes show missed firings with narrow pulses on inductive loads; long pulses resolve this.

Why Other Options Are Wrong:

“True” contradicts standard practice; conditions like “only at small α” or “only resistive load” add constraints not given and are not generally reliable for inductive cases.

Common Pitfalls:

Assuming gate triggering is identical for R and R–L loads; overlooking latching/holding current requirements.

Final Answer:

False