Are you ever confused with the words AC and DC w.r.t. power supplies?

If YES, then this page is for you. Just go through this page slowly and get an idea about DC power supply. Hay, there is NO EXAM afterwards. Nobody is behind you to check. Relax.

If NO, just go through the highlighted words quickly. If you want to know about any highlighted word, then read slowly.

Actually, the name DC (Direct Current) is a misnomer. Some people may think, the power supply, which is available directly to home or office is Direct Current (DC) supply. NO. it is AC supply only.

If you consider the behavior of current flow in DC supply, its name shall be either Uni-directional Current supply or Non-Alternating Current supply.


Okay, coming to our topic, DC supply is the power supply normally available from batteries, which have fixed positive and negative polarities, which will never change the direction of current flow. i.e., current flows from positive terminal to negative terminal. Where as the electrons flow from negative terminal to positive terminal (Current Electricity).

OHM's law applies easily for DC power supplies.

i.e., V=I*R or I=V/R or R=V/I

where, V=voltage, I=current flow and R=Resistance.

In electronic circuits, most of the times, we use DC power supply only. The DC power may be drawn from Batteries or rectified AC power supply. Many methods are available to convert AC power supply to DC power supply, out of which, Rectifier circuit and SMPS (Switching Mode Power Supply) are highly used.


In general, DC power supplies have two or three types of voltage levels.

  1. Positive (+ve) Voltage level

  2. Negative (-ve) Voltage level

  3. Ground (gnd) level

Positive Voltage is known for higher potential, where Negative Voltage is known for lower potential. Ground is the reference for both the Positive and Negative Voltage levels, which lies between the positive and negative voltages.

Some times, like batteries and cells, where only two terminals are available from the power source, the ground and negative terminals are called by any name as ground or negative. Where as positive terminal is called as positive only.


Actually, the voltage levels mentioned above are relative voltage levels to each other. If you observe the figure below, four cells are arranged in series, each with 1.5Volts DC. Each cell is marked as +ve and -ve on both the ends. You may observe that, by selecting the connections (CN1 to CN5) as ground reference, the Positive and Negative Voltages vary.

For easy understanding, ground level may be the basic reference level marked as 0V and the voltage above the reference may be considered as positive voltage and the voltage below the reference may be considered as negative voltage.

So, the total voltage difference between the positive to negative terminal may be considered as arthmatic summation of positive and negative voltages.

eg: Total voltage between CN4 and CN1 in any case is 4.5V only.


DC power supplies are highly used in electronic circuits and mechatronics projects.  Most of the cases, the DC Desktop power supply is used, which is derived from mains power supply (after rectification and filtration) for testing, then connect to battery power supply for final project.

AC to DC adaptors are used for economical and easy DC power supply for our projects or Battery packs, based on the required voltage and current.

Now-a-days, rechargeable batteries, (like Lithium-Ion, LiPo, LiFePo4 etc.) are affordable for the electronics and mechatronics projects