How Does an AC Circuit Differ From a DC Circuit?

AC circuits can use capacitors and inductors.

In a DC circuit, current flows steadily in one direction. Current in an AC circuit flows back and forth. While direct current (DC) circuits are simpler, those that use alternating current (AC) are more sophisticated and versatile.

Reactive Components

DC circuits may use resistors, transistors and diodes. AC circuits can use these and also reactive components such as transformers, inductors and capacitors. A transformer can efficiently increase or decrease AC voltage. Capacitors and inductors filter out unwanted AC signals.

RMS Power

You can calculate DC power easily by multiplying volts times amps to get watts. In an AC circuit, power is more complicated because the voltage and current oscillate back and forth. Here, you find power by using a root mean square (RMS) calculation, which gives a time-averaged figure. You multiply volts times amps, then multiply the result by .707, or 1 divided by the square root of 2.

Distortion

AC circuits usually run from 120 volt 60 cycle household power, produced as a fairly pure sine wave. Complex AC circuits such as fluorescent lighting ballasts can distort and roughen the sine wave, creating problems for other equipment plugged into other outlets.

References

• Hyperphysics: DC Power
• Hyperphysics: AC Power
• Ace Ballast: Frequently Asked Questions