A step down chopper operates from a $$D.C.$$ voltage source $$V_s = 400 V$$ and feeds a $$DC$$ motor armature with a back emf $$E_b = 300 V$$. From the oscilloscope traces it is found that the current rises for a time $$t_r = 10$$ m sec and falls to zero over time $$t_f = 5$$ m sec and remains zero for a time of $$t_o = 6$$ m sec in every chopping cycle. Then, average $$DC$$ voltage across the freewheeling diode will be