We use both AC and DC current on a daily basis for digital electronics and various power outlets. However, people still don’t know the basic differences between these two, and why we need both.
With that in mind, we’re going to examine some of the key differences between AC and DC, as well as talk about their use in our everyday lives.
Alternating Current (AC)
Alternating Current is nothing more than a periodical change in direction of the flow of charge. Simply put, alternating current is here to describe the flow of the electricity through the conductor. As its name suggests, the flow of the current is periodically changed, reserving the voltage level along with it. Alternating Current is supplied to households and office buildings and can be converted to direct current if needed.
Can you generate an Alternating Current? Of course, you can. The most popular device for generating AC is called an alternator. Inside the alternator is a magnetic field as well as a loop of wire which is spun inside, used for the current induction. To produce the current, this wire needs to have some kind of rotation, which can be produced by flowing water, steam turbine, or wind turbine. During the spinning process, the wire periodically changes its magnetic polarity which makes both current and the voltage alternate.
When it comes to the waveforms, an Alternating Current is vastly different from a Direct Current. As you’ve probably guessed, AC waveforms come in a form of a sine wave. This can be seen easily if we connect the oscilloscope to a circuit with the Alternating Current. Here, we can see a couple of waveforms in which the sine wave is the most common. In most cases, an Alternating Current that you use in your home has the exact same sine wave. This indicates that the amplitude of the current flow changes over time, which is exactly what an Alternating Current is.
Since we mentioned different types of waveforms, it’s important to mention the square wave. The square wave is often used in switching and digital electronics for testing purposes. This type of wave indicates that the amplitude stays the same for a period of time, before dropping to a negative value and stays there for the same period of time. The process repeats during the operation.
Finally, we have a triangle wave, which is a bit less common. It’s mainly used for testing amplifiers and other linear electronics.
As we mentioned earlier, AC is used in our homes and offices. The main benefit of Alternating Current is that it can be easily generated and transported across long distances thus being the number one choice for the aforementioned purpose. Just imagine having to supply a whole city or a part of the city using a single power plant. AC makes it possible – it’s fast and it’s easily generated. On top of that, power plants can use transformers to convert to/from high voltages if needed. The higher the voltage is, the lower the current, producing less heat in the power line.
Many household appliances such as refrigerators and dishwashers also use AC. AC is able to power electric motors which convert this electrical energy into mechanical energy (rotation, translation, torque, etc).
Direct Current (DC)
Direct Current is much easier to grasp since it’s a completely different term from alternating current. While alternating current is going back and forth, direct current provides a constant current in a single direction. The most common example of direct current is a battery in your flashlight or a smartphone, as well as a PSU (Power Supply Unit) in your PC.
DC can be generated in numerous ways. The most common component used is called the rectifier. A rectifier is exactly what it sounds like. Just imagine the sine wave that needs to be rectified or straightened to look like a waveform of the Direct Current. It has electronic or electromechanical elements that let the current flow in one direction. Alternatively, a typical AC generator with commutator can also produce direct current, as well as batteries that produce DC due to chemical reactions inside them.
Direct Current has only one waveform consisting of a straight horizontal line. This line represents the change (or the lack of change) of voltage over time. In practice, the intensity of the voltage and the current may change but the direction of the flow stays the same. Some DC sources can’t produce this kind of plot all the time, with the typical example being batteries. Over time, they lose their power and the voltage will start dropping at some point, producing a different plot. For the most time, we can assume that the plot looks exactly as we described it – a straight horizontal line that shows constant voltage.
The direct current is used by small electronics such as smartphones, flashlights, and computers. That’s why you need a special power supply in your computer – for converting AC to DC. Other typical applications include TVs, as well as new-generation electric vehicles since they use rechargeable batteries as power supplies.
Both AC and DC have their own purposes and you can’t say that one is better than another. While AC is suited for our households due to its ease of generation and distribution, DC is the only way of powering battery-based electronics and electric cars. Despite the huge popularity and implementation of Alternating Current, most of the electronics we use to take advantage of Direct Current, meaning that we need both of them equally.