AC and DC: Everything you need to know about AC Power and DC Power

In this article, you'll learn what the difference between AC (Alternating Current) power and DC (Direct Current) power is.

There are two types of current/voltage – AC (Alternating Current) and DC (Direct Current). Thus, when you are working with electronics, you must know about those two types. Therefore, this article will teach you about the differences between AC and DC, how they work, as well as some additional facts.

What is AC (Alternating Current)?

In short, AC is current/voltage that changes over time. This type of power is the one that comes out of the sockets inside and around houses. If you drew a Voltage-Time graph, it would look something like this sine wave:

AC and DV - AC sine wave

As you can see in this graph, the voltage changes over time and even gets into the negative region. As a result, the voltage, the polarity, and the flow of the electrons (current flow) change.
Because of the alternating current flow, we cannot store Alternating Current.

If we talk about the voltage of an alternating current, we refer to the maximum voltage the sine wave reaches.

In the following, I am going to explain what the frequency of AC power means.


The frequency determines how often a cycle repeats within a second. The frequency is measured in Hz (Hertz).
For instance, the frequency of the graph above is 1Hz because it has exactly one cycle per second.

The usual frequency of AC power in houses is between 50Hz and 60Hz. Due to that high frequency, we cannot see our lights flicker even though the voltage changes all the time.

Examples for AC

What is DC (Direct Current)?

In short, DC, compared to AC, is a current/voltage that “doesn’t change” over time. This means that the power source doesn’t change its polarity. For example, the voltage of a usual AA battery drops over time. However, the AA battery is still considered a DC source as it doesn’t change its polarity.
The following image shows a simplified Voltage-Time graph of a DC source that drops in voltage over time and a DC source that is completely steady:

AC and DC - DC power source
Examples for DC
  • Batteries
  • Electric Vehicles
  • Different kinds of electric motors
  • Computer
  • Charger for your phone

How to convert AC to DC?

We can convert AC to DC with a very simple circuit that consists of 4 diodes and a capacitor. Such a circuit is called a rectifier.
The circuit for a simple rectifier looks like this:

rectifier circuit

We use four diodes to remove the negative voltages and turn them into positive values. However, only the four diodes would give us a Time-Voltage graph like this one:

To fix this problem and get an almost constant current, we simply need to add one or multiple capacitors like in the circuit above. Now, the result should look something similar to this:

Disclaimer: If you decide to build this circuit on your own, always have a look at the specifications and limits of your components. Building this circuit is at your own risk!


In conclusion, AC (Alternating Current) changes its polarity over time, whereas DC (Direct Current) does not. Additionally, AC changes its voltage in form of a sine wave, whereas DC does not change its voltage or, at least, doesn’t get into negative values.

We can convert AC to DC with a rectifier and DC to AC with an inverter.


Alternating Current (AC)Direct Current (DC)
  • Changes polarity over time (electrons move in both directions)
  • Can’t be stored
  • Comes out of the sockets in houses or other buildings
  • Used to deliver electricity over long distances
  • Can be rectified into DC using a rectifier
  • Does not change polarity (electrons move in only one direction)
  • Can be stored in batteries
  • Usually, buildings do not provide DC sockets
  • Harder to deliver over long distances as it quickly loses energy
  • Can be inverted into AC using an inverter


Thanks for reading!

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