When AC voltage of a fixed frequency and voltage as shown in figure "D' is applied to the input of the single phase controlled rectifier shown in figure "C", what determines the average DC current output value as controlled at any given time? See illustration EL-0154.
• Single-phase controlled rectifier (thyristor/SCR) operation with a fixed AC input (figure C + D) • Relationship between firing (delay) angle α and the average DC output current I_DC (figure E) • Difference between pulse timing, pulse frequency, and gate voltage level in SCR control
• Look at figure E: how does shifting the shaded conduction portions along the AC waveform change the average (dashed) DC level? • If the AC frequency and amplitude in figure D stay constant, what is the only thing the control circuit in figure C can vary from cycle to cycle? • Does an SCR/thyristor need gate voltage all the time to conduct, or just a trigger at a particular point in each AC half‑cycle?
• Verify which choice directly affects the delay angle α (firing angle) shown in figure E. • Eliminate any options that would not change where in the AC waveform the device turns on. • Confirm that in a line‑commutated SCR rectifier, once triggered in a half‑cycle, the SCR naturally turns off when current falls to zero, not when gate voltage is removed.
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