AC / DC

AC and DC refer to the type of current flow through a circuit. AC stands for Alternating Current and DC stands for Direct Current.

Alternating Current (AC)

Alternating current describes a charge that flows in one direction, then periodically switches direction. The voltage also reverses along with the current and swings continually between positive (+) and negative (-). A 12V AC current alternates between +12V and -12V. When plotted on a graph, AC resembles a sine wave.

The rate of direction change is called the frequency, which is measured in hertz (Hz). One hertz is the number of positive/negative cycles per second. The mains electricity in the US is measured at 60Hz and 120V.

Direct Current (DC)

Unlike Alternating Current, Direct current flows in only one direction, and likewise, a DC voltage is always positive (+) or always negative (-). The voltage and current may increase or decrease, but the direction stays the same.

All electronic circuits that we build require a steady DC at a consistent value in order to operate correctly. Batteries and regulated power bench supplies are the best choices for providing a steady DC supply for your circuits.

Power Supplies

Power supplies are able to convert the mains AC supply into a safer low voltage AC current. It does so through the use of a transformer. The lower voltage AC is then turned into DC through a bridge rectifier. The signal at this point looks like if you've flipped all the peaks of the AC sine curve to one direction. This state is called Varying DC and it's not yet suitable for use in electronic circuits.

Varying DC can be smoothed with the aid of a capacitor. Smooth AC is suitable for projects that have are not very sensitive to voltage variations such as lamps, heaters and motors.

• Steady DC
• Smooth DC
• Varying DC

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References:

https://learn.sparkfun.com/tutorials/alternating-current-ac-vs-direct-current-dc/all

https://electronicsclub.info/acdc.htm#props

https://cdn.sparkfun.com/assets/home_page_posts/2/7/7/5/SFE_Poster_Series_-_AC_and_DC.pdf