Briefly explain how the output voltage/current is unidirectional.
The ac to be transformed is connected across the primary (P1P2) of a transformer. In the first half of the cycle, suppose P1 is positive and P2 is negative. This makes S1 of the secondary coil positive and S2 negative. As a result, the diode D1 will be forward biased, and hence, it will conduct. The current flows through D1 and from X to Y through RL and we get an output. In this cycle, the diode D2 does not conduct as it is reverse biased. Similarly, in the second half of the cycle, D1 does not conduct but D2 conducts. However, the current flows from X to Y again. Hence, in the entire process, the current flows in one direction itself.