Question

why cannot transistor act as a rectifier

Answer 1

 A transistor has a P and N type material that are joined, a junction, as well as another junction with one of the two mentioned types of semiconductor. Across these junctions they are essentially the same a a diode. Within power limitations of the junction the can rectify an alternating current. Some devices are designed specifically for these purposes and are therefore the obvious choice of designers. Hope this is of some help.Source(s):Electronics tech by trade.