A step down chopper operates from a DC voltage source Vs and feeds a DC motor armature with counter emf Eb. From oscilloscope traces it is found that current increases for time tr, falls to zero over a time tf and remains zero for a time to in every chopping cycle. Then the average voltage across the motor would be
- A. Vs·tr / (tr + tf + to)
- B. (Vs·tr + Eb·tf) / (tr + tf + to)
- C. (Vs·tr + Eb·to) / (tr + tf + to)
- D. (Vs·tr + Eb(tf + to)) / (tr + tf + to)