This arrangement uses two transistors having complementary symmetry (one transistor is PNP and the other is NPN). The term complementary arises from the fact that one transistor is NPN type and the other is PNP type. For better current driving capability and low impedance darlington transistors arre used. During the positive half-cycle, the NPN transistors are switched on while the PNP transistors remain reverse biased. This results in a half cycle of output voltage across the load. Similarly the PNP transistors are forward biased in the negative half-cycle.