The usefulness of AC and DC can be seen everyday at home, at the office, at work, and more in public and private places. General magnitudes AC (Alternate Current) and DC (Direct Current) is the same as the voltage (volts), current (Ampere), and power (Watts) but has a very different signal shape when viewed using an oscilloscope.
In addition, the usefulness of AC and DC can be seen in equipment that uses both the power source. Many electronic appliances that use a low current DC power source such as a cell phone, flashlight, remote control, MP3 player, MP4 player, a camcorder, pocket radios, and digital cameras. While the washing machine, electric water pumps, irons, lamps and lighting, which are still using the AC power source.
From the example above, there are several devices that can use AC and DC source like a flashlight that can light up if connected to a source of AC or DC voltage, the motor can spin if given voltage AC or DC.
AC and DC can be transformed or converted to each other using electronic circuits. AC to DC Converter circuit is useful to convert the AC voltage into DC, while DC to AC Converter circuit is useful for converting DC voltage into AC. The circuits not only can convert the power source but also can adjust the amount of output produced.
One example of DC to AC Converter is a UPS (Uninterruptible Power Supply) which is used as a backup power source when the power fails. Battery as a DC voltage source 6 Volt or 12 Volt contained in the UPS will turn into a 220-240 Volt AC voltage after the conversion process. If the source of power is on again, then the voltage of 220-240 Volt AC will handle the load and perform battery charging.
Generally, equipment that uses AC power source is bigger while the equipment that uses a DC power source is smaller but it is not absolute. The usefulness of AC and DC as power source can easily be seen in the large factories that use motors AC high voltage but the controlling circuit uses a low current DC voltage source.
Many textile industry has been using high-power AC motor with an AC voltage source but it does not come directly from the main power but from a device called a motor inventer. This motor inverter converting the AC voltage into DC and then change it again with a different frequency. The change is intended to set the frequency of rotation of the motor, especially a three-phase electric motor. The smaller the frequency, the slower the rotation of the motor and vice versa.
Another example, mobile phone charger, modem adapter, switch adapter and laptop power supply is a DC power source. The DC power sources are not really pure DC like a battery but a change of AC into DC by a device called the DC regulator. Power supply regulator circuit lowers AC power source using step-down transformer becomes smaller (as needed) and then convert it into DC. DC regulators can also be referred to as AC to DC Converter.