On-state voltage behavior of a conducting thyristor When a thyristor is conducting (on-state), how does the anode–cathode voltage drop vary with increasing load current?

Introduction / Context:Designers often approximate a conducting thyristor as a small fixed drop (like a diode). In reality, the on-state voltage has a fixed component plus a component proportional to current, described by the device’s on-state dynamic resistance.

Given Data / Assumptions:

• Thyristor is fully turned on and remains in conduction region.
• Temperature and device type affect exact values but not the trend.

Concept / Approach:The on-state characteristic of an SCR can be modeled as V_on ≈ V_T0 + r_on * I, where V_T0 is the threshold-like component and r_on is the slope (dynamic) resistance. As current rises, the r_on * I term increases the total drop slightly.

Step-by-Step Solution:Assume V_on = V_T0 + r_on * I.For higher I, the r_on * I term grows.Therefore, V_on shows a slight upward trend with current.

Verification / Alternative check:Manufacturer V–I curves confirm a non-zero slope in the conduction region; tabulated on-state voltage is typically specified at a rated current (for example, 1.6 V at I_T).

Why Other Options Are Wrong:

• Absolutely constant ignores dynamic resistance.
• Decreasing voltage with more current contradicts observed characteristics.
• “None of the above” is invalid because (c) is standard behavior.

Common Pitfalls:

• Using a pure constant-drop model in loss calculations underestimates conduction losses at high current.

Final Answer:It increases slightly with increasing current (due to on-state slope resistance)