A single phase half wave controlled rectifier circuit has an R-L load....
Free wheeling diode is forward biased only when SCR is reverse biased.
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A single phase half wave controlled rectifier circuit has an R-L load....
Explanation:
In a single-phase half-wave controlled rectifier circuit with an R-L load, a freewheeling diode is used to provide a path for the inductive load current when the thyristor is turned off. The freewheeling diode is connected in parallel with the load and in series with the inductor.
When the SCR is conducting:
During the positive half-cycle of the input voltage, the SCR is forward biased and conducts current. The load current flows through the SCR and the load resistor, resulting in rectification of the input voltage.
When the SCR is turned off:
When the SCR is turned off, the inductive load tends to maintain its current flow due to its inductance. This causes a reverse voltage to appear across the SCR, which can damage the device if it is not controlled. To provide a path for this inductive current, a freewheeling diode is connected in parallel with the load.
Working of the freewheeling diode:
When the SCR is turned off, the voltage across the load is reversed. The freewheeling diode becomes forward biased and conducts the inductive load current. This allows the energy stored in the inductor to dissipate in the load resistor and the diode, preventing any damage to the SCR.
Conclusion:
Therefore, when the freewheeling diode is conducting, it is reverse biased with respect to the input voltage. This is because the voltage across the diode is in the opposite direction to the forward-biased voltage of the SCR during conduction. Hence, option 'B' is the correct answer.