Circuit Operation

A circuit with a single diode and an RL load is shown above. The source v_s is an alternating sinusoidal source. If v_s = E * sin (wt), v_s is positive when 0 < wt < p, and v_s is negative when p < wt <2p. When v_s starts becoming positive, the diode starts conducting and the positive source keeps the diode in conduction till wt reaches p radians. At that instant defined by wt = p radians, the current through the circuit is not zero and there is some energy stored in the inductor. The voltage across an inductor is positive when the current through it is increasing and it becomes negative when the current through it tends to fall. When the voltage across the inductor is negative, it is in such a direction as to forward-bias the diode. The polarity of voltage across the inductor is as shown in the sketches shown below.

When v_s changes from a positive to a negative value, there is current through the load at the instant wt = p radians and the diode continues to conduct till the energy stored in the inductor becomes zero. After that the current tends to flow in the reverse direction and the diode blocks conduction. The entire applied voltage now appears across the diode.