# AC And DC Circuit Theory

**DC Circuits**

Direct Current or D.C.(more commonly referred) is a voltage or current that flows in unidirectional way in a circuit. It has a fixed amplitude(magnitude) and a specific direction associated with it. For example +5V represents 5 volts in positive direction and -3.3V represents 3.3V in negative direction. Common sources of DC currents and voltages are produced by power supplies, batteries etc.

As we know now, DC power supplies don’t change their values with respect to time, they have a fixed value flowing in unidirectional. In other words DC power supplies maintain their value all the time and never change their direction unless the connections are reversed. A simple DC circuit is shown in figure 1.

**AC Circuits**

An Alternating Current or A.C.(more commonly referred) is a voltage or current that varies in both amplitude(magnitude) and direction with respect to time making it bi-directional. AC function can be represented by a power supply or signal generator that follows the mathematical equation given by

The waveform obtained by plotting the instantaneous values of voltage or current against time is called AC waveform. An AC waveform constantly changes its polarity every half cycle alternating between positive max peak and negative max peak respectively with respect to time. The main characteristics of AC waveform are

**The Period(T)**is the time taken by the waveform in seconds to repeat itself from start to finish. It is also called*Periodic Time*for sine waves and*Pulse Width*for square waves.**The Frequency(f)**is the number of times the waveform repeats itself within one second time period. It is the reciprocal of*Period(T),*with the unit of measurement being**The Amplitude(A)**is the magnitude or amplitude of the signal waveform measured in*volts*or amps.