The DC voltage symbol is used to represent a direct current (DC) voltage source or supply in electrical and electronic schematics and diagrams. It indicates that the power supply provides a constant DC voltage that does not alternate like AC power. Understanding what the DC voltage symbol represents helps when reading schematics and wiring diagrams.
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The Appearance of the DC Voltage Symbol
The DC voltage symbol consists of a straight line parallel to a curved line. The straight line represents the positive or + side of the supply, while the curved line represents the negative or – side. The lines are approximately equal in length. Sometimes the symbol may just consist of the two parallel lines without the + and – symbols at the end.
For example:
| DC Voltage Symbol | + | —— | — | – |
The DC voltage symbol is often drawn with slightly longer lines coming out of the + and – sides. These indicate where other components would connect to the positive and negative terminals of the power supply in a circuit diagram.
Difference Between DC and AC Voltage Symbols
The key difference between the DC and AC voltage symbols is that the DC symbol has straight parallel lines, while the AC symbol uses curved or sinusoidal lines. This represents how DC voltage is constant, while AC voltage alternates between positive and negative over time in a waveform pattern.
The AC voltage symbol consists of a curved line that peaks above and dips below a straight line in the middle. For example:
| AC Voltage Symbol | ~ | ) | ( |
Being able to quickly recognize the difference between these symbols is important for understanding circuit diagrams and electrical schematics.
Meaning and Use of the DC Voltage Symbol
The DC voltage symbol is used to indicate any source of constant DC voltage or power in a circuit. This may be:
- A battery or cell
- A DC power supply
- The DC output from a rectifier circuit
- The positive and negative terminals on electronic components and devices
The symbol tells you that the voltage at that point is DC rather than alternating current (AC). It gives important information about how that part of the circuit will function.
Batteries and DC Power Supplies
When the DC symbol is used to represent a battery, it will usually have + and – signs included to indicate the polarity. Multiple cells may be drawn in series to represent higher voltage batteries. For DC power supplies, the voltage level may be indicated, like +12VDC. This tells you the supply provides a steady 12V DC output.
Rectifiers
The DC symbol is used at the output of rectifier circuits and power supplies. A rectifier converts AC into pulsating DC. The DC voltage symbol indicates that downstream of that point, the circuit sees a DC input rather than AC.
Component Terminals
Many electronic components like transistors, integrated circuits, and resistors have positive and negative terminals that require DC voltage. The DC symbol lets you know how to connect the DC power correctly to the device. The + and – markings indicate which terminal gets the positive voltage.
Schematic Symbols Similar to the DC Voltage Symbol
There are some other common electrical and electronic symbols that look similar to the DC voltage symbol but represent different components or functions:
Ground
The ground symbol is a horizontal line with three diagonal lines below it. This represents the ground reference point in a circuit. It connects to zero volts rather than a DC power source:
| Ground Symbol | — | // | // | // |
Diode
A diode symbol uses a triangle pointing in the direction of conventional current flow, with a vertical line on one side:
| Diode Symbol | |> |
This resembles the DC symbol but does not have two parallel lines of equal length.
NPN Transistor
An NPN transistor symbol uses an arrow and a straight line just like the DC symbol. But it includes an additional diagonal line on one side and omits the + and – markings:
| NPN Transistor Symbol | \ | | | —> |
Conclusion
The DC voltage symbol, represented by two parallel lines of equal length, is used to indicate a source of constant DC power or voltage in electrical and electronic diagrams. It is an important basic symbol that engineers and technicians refer to when analyzing circuits. Recognizing the symbol and understanding its meaning in terms of DC power allows for proper circuit design, troubleshooting, and analysis.