AC/DC regulated switching power supplies have similar applications as AC/DC regulated transformer adapters. In contrast to the transformer power supplies they are well protected against overload and short-circuit. They have a smaller size and weight. The mains voltage is rectified and converted to DC. The Pulse Width Modulation (PWM) generates a voltage of a frequency 50-200kHz. This allows a significant reduction in copper loss, since the number of turns of the transformer decreases with increasing frequency. The secondary voltage is rectified, filtered and is then transmitted directly to the load. In order to regulate the voltage the output current and voltage are measured and then the pulse duty factor of the signal that controls the keying on the primary side of the transformer changes accordingly. The keying on the primary side (called primary switching), where there’s high frequency, requires a smaller transformer as compared with the 50Hz transformer. Until recently, only switching power supplies were used in high-tech systems. Rising energy costs, the increasing miniaturization of devices and increasing demands of users have made the switch mode power supplies are becoming increasingly common. High efficiency (reaching up to 90%) and stable output voltage independent of the supply voltage quality makes them almost an ideal source of direct current. They support a wide range of equipment: computer peripherals, consumer electronics, telecommunications and medical equipment.