Question

In controlled rectifiers, the nature of load current, i.e. whether load current is continuous or discontinuous:

• A. does not depend on type of load and firing angle delay
• B. depends both on the type of load and firing angle delay
• C. depends only on the type of load
• D. depends only on the firing angle delay

Hint:

Discontinuous current often occurs with resistive loads or large firing angles. For smooth DC, aim for inductive loads and small $\alpha$.

Answer 1

The Correct Option is B

Step 1: Understanding Load Current in Controlled Rectifiers
In a controlled rectifier, the load current may either be continuous (never reaches zero) or discontinuous (falls to zero during part of the cycle). Whether the current is continuous or discontinuous depends on two major factors:
Nature of the load: Resistive, inductive, or capacitive.
Firing angle ($\alpha$): The point in the AC cycle where the SCR or controlled device is triggered.
Step 2: Type of Load
- For a pure resistive load, the current follows the voltage waveform closely and falls to zero every half cycle.
- For inductive loads, energy is stored in the magnetic field and released after the source voltage becomes zero, helping the current continue even without source voltage — supporting continuous conduction.
Step 3: Effect of Firing Angle
- A large firing angle (delayed conduction) reduces the conduction interval.
- At larger angles, the voltage available to build up current is reduced, making it more likely for current to drop to zero before the next firing pulse — leading to discontinuous conduction.
Step 4: Combined Effect
Both the load’s energy storage capability (e.g., via inductance) and the firing delay influence whether the current will remain continuous. Hence, both must be considered. Conclusion:
The current nature (continuous/discontinuous) in controlled rectifiers depends on both load type and firing angle — Option (2) is correct.