Circuit Operation

Let the source voltage v_s be defined to be E*sin (wt). The source voltage is positive when 0 < wt < p radians and it is negative when p < wt < 2p radians. When v_s is positive, diode D₁ conducts and the voltage v_c is positive. This in turn leads to diode D₂ being reverse-biased during this period. During p < wt < 2p, the voltage v_c would be negative if diode D₁ tends to conduct. This means that D₂ would be forward-biased and would conduct. When diode D₂ conducts, the voltage v_c would be zero volts, assuming that the diode drop is negligible. Additionally when diode D₂ conducts, diode D₁ remains reverse-biased, because the voltage v_s is negative. When the current through the inductor tends to fall, it starts acting as a source. When the inductor acts as a source, its voltage tends to forward bias diode D₂ if the source voltage v_s is negative and forward bias diode D₁ if the source voltage v_s is positive. Even when the source voltage v_s is positive, the inductor current would tend to fall if the source voltage is less than the voltage drop across the load resistor. During the negative half-cycle of source voltage, diode D₁ blocks conduction and diode D₂ is forced to conduct. Since diode D₂ allows the inductor current circulate through L, R and D₂, diode D₂ is called the free-wheeling diode. We can say that the current free-wheels through D₂.