a switching power supply uses zero - current and zero - voltage switching to reduce switching noise . a main switch and an auxiliary switch channel current and voltage between various component paths to maintain a dc output voltage while switching in zero - current or zero - voltage states . switch on - off time ratios are controlled with a simple scheme to improve the circuit power factor . the switching rate can be set to arbitrary frequencies , with switch on time and off time being controlled independently . this scheme permits efficient driving of a load that is substantially less than the rated load , as generally found in portable tv circuits . the switches and control functions can be implemented on an integrated circuit .