The unidirectional flow of an electric charge through conductors is known as direct current, DC. Once the current is established, the DC voltage and current are both constant in time. Mobile batteries, flashlights, and electric vehicles are examples of devices that use direct current to supply power to electrical devices. Alternating current, AC, is when the flow of electric charge changes direction periodically. Any device that produces alternating current is known as an AC source. Most electrical appliances, like bulbs, fans, motors, etc., work on alternating current. The waveform of alternating current can be sinusoidal, triangular, or square wave, with the positive half period corresponding to the current's positive direction, and the negative half period reversing. The peak value of the wave in both directions is called the amplitude, while the time interval between the two successive cycles is known as the time period, and the number of cycles per second is the frequency. A rectifier converts alternating current into direct current, whereas an inverter converts direct current into alternating current.