In a single-phase half-bridge inverter, two main thyristors (or switches) operate with complementary gating. What is the phase displacement between their gate pulses for ideal 50% duty operation?

Introduction / Context:
Half-bridge inverters are foundational DC–AC conversion circuits. They produce a two-level output by alternately turning on two complementary switches, creating a square wave across the load. The required phase displacement between gate signals ensures non-overlap conduction and correct waveform generation.

Given Data / Assumptions:

• Single-phase half-bridge inverter with two complementary devices.
• Ideal devices and dead-time negligible for the concept.
• Target: 50% duty each to synthesize a square wave.

Concept / Approach:
For a half-bridge, when the top device is ON, the output is approximately +V/2 (with a split DC bus). When the bottom device is ON, the output is approximately -V/2. To achieve this alternating pattern, the gate pulses must be 180° apart in phase so that one is ON while the other is OFF.

Step-by-Step Solution:
1) A full electrical cycle is 360°.2) Each switch should conduct for approximately 180° to achieve a 50% duty square wave.3) Therefore, the turn-on instants of the two switches differ by 180°.
Verification / Alternative check:
Observe the output waveform polarity: positive half-cycle when the top device conducts, negative half-cycle when the bottom device conducts. These halves must be sequential and not overlapping, hence 180° separation.

Why Other Options Are Wrong:

• 60°, 90°, 120°: These would distort the duty ratio and either force overlap or gaps, not delivering the intended two-level square wave.
• None of the above: incorrect because 180° is the standard for complementary operation.

Common Pitfalls:

• Confusing half-bridge with full-bridge timing where legs are also 180° apart but applied to two legs.
• Ignoring dead-time; while needed in practice, it does not change the nominal 180° separation.

Final Answer:
180° (Option D).