Power Supply Symbols Chart: A Complete Guide to AC, DC, Ground, Battery, and Source Symbols

Power supplies are one of the most fundamental parts of electronic circuits. When reading a schematic, you may encounter different power-related symbols, including AC sources, voltage supplies, and ground references.

Although some symbols look simple, each one represents a specific electrical function. Misunderstanding these symbols can lead to incorrect connections, unexpected circuit behavior, or even EMC issues in PCB designs.

In this guide, you will learn:

• The full power supply symbol chart, from DC and AC sources to batteries
• How earth, chassis, and signal ground symbols differ
• Why do dependent sources use a diamond instead of a circle
• Where IEC and ANSI symbol conventions disagree
• How each symbol maps to a real PCB footprint

Figure: A complete power supply symbol chart

Power Supply Symbols Chart (Quick Reference)

Fourteen symbols cover almost every power source you will meet on a schematic. They split into four families: sources, batteries, grounds, and rail labels.

What Is a Power Supply Symbol?

A power supply symbol is a standardized graphical symbol used in schematics to represent a power source, supply rail, or reference connection.

Instead of using lengthy written descriptions, these symbols allow engineers to identify electrical functions quickly and consistently.

Depending on the symbol type, power-related symbols can communicate several types of information:

• Source type: Whether the circuit uses a DC source, AC source, battery, or dependent source.
• Polarity/direction: What is the positive terminal or the direction of conventional current flow?
• Reference role: If the node is a supply, return or safety connection.

The symbol itself does not define current rating, regulation performance, or physical specifications. Those live in the reference designator, the value field, and the bill of materials.

DC Power Supply Symbol

The DC power supply symbol is a circle containing a plus sign at one terminal and a minus sign at the other. It represents a source that holds one terminal at a higher potential than the other, with no reversal over time.

Figure: The DC power supply symbol marked positive and negative terminals.

Circle With Plus and Minus Terminals

The circle is the source body. The plus and minus marks sit inside or immediately beside the terminals, and they define the reference polarity for every calculation on the sheet. Reverse the marks and every node voltage derived from that source changes sign.

The Line-and-Dash DC Mark

On equipment labels, panels, and power bricks, you meet a different glyph: a solid horizontal line above a dashed line, defined as IEC 60417-5031. It means direct current. It is a marking, not a schematic symbol, so it belongs on a silkscreen or a rating plate rather than in a netlist.

DC Voltage Source vs DC Current Source

Both are circles, and the contents tell them apart. Plus and minus marks make it a voltage source. A single arrow through the body makes it a current source, and that arrow points in the direction of conventional current.

AC Power Supply Symbol

The AC power supply symbol is typically drawn as a circle containing a sine wave. It represents an alternating voltage source where polarity changes periodically over time. Unlike a DC source, neither terminal remains permanently positive or negative, so fixed + and − polarity markings are not used.

Figure: AC power supply represented by a circle with a single sine wave.

Single-Phase AC Source Symbol

A single-phase AC source symbol consists of a circle containing a sine wave with two connection terminals.

AC sources are indicated by values next to them as RMS voltage and frequency, such as 230 V and 50 Hz. The symbol does not indicate the amplitude of the signal; an unlabeled AC source is an incomplete diagram.

Symbols for Three-Phase and Mains Inlet

Three-phase supplies are modeled as three independent single-phase supplies with the phase designation, in wye or delta configuration.

An AC mains input is usually shown as a connector or terminal entry point rather than a standalone AC source symbol. Practical circuits often include protection components such as fuses, filters, and surge protection near the mains input.

Upstream of a rectifier from an AC source is the first place where your board becomes a high-voltage design and requires creepage and clearance rules. Consider all input-side components as a critical section.

Battery Symbols: Single-Cell vs Multi-Cell

Figure: Single-cell and multi-cell battery symbols

A battery symbol is a pair of parallel bars of unequal length, and the rule never changes: the long thin bar is the positive terminal, the short thick bar is negative. One pair is one cell. Repeated pairs are cells in series.

A long series stack is rarely drawn cell by cell. Most schematics show two pairs, a dotted break, then a final pair, with the total voltage written alongside. That shorthand keeps the sheet readable without hiding the series connection.

Note: The bar lengths carry the polarity, not the order in which you drew them. If your library symbol has equal-length bars, fix the library. An equal-bar battery is ambiguous, and an engineer reviewing your schematic will flag it.

Ground Symbols: Earth, Chassis, and Signal Ground

Figure: Earth, chassis, and signal ground symbols

Ground symbols identify a circuit's reference potential or a connection to earth, chassis, or another designated ground network. They may also provide a return path, depending on the circuit and grounding scheme.

These ground symbols represent different functions and should not be treated as interchangeable.

Chassis Ground Is Not Earth Ground

The distinction matters because a chassis is not automatically at earth potential. IEEE 315 clause 3.9.2 notes explicitly that a chassis or frame may sit at a substantial potential relative to the earth around it. If you want them bonded, draw the bond as a deliberate connection with its own designator.

AGND, DGND, and PGND Named Returns

Named variants such as AGND, DGND, and PGND all reuse the signal ground triangle. The shape stays identical and only the label inside changes, which is what allows a layout tool to keep three separate returns and join them at one defined tie point.

Constant Voltage Source vs Constant Current Source Symbols

Figure: Constant voltage source symbol vs constant current source symbol

Both symbols are typically drawn as circles, but their internal markings distinguish the two source types.

A constant voltage source maintains a specified terminal voltage while the load determines the resulting current. A constant current source maintains a specified current while the load determines the resulting terminal voltage.

Why Ideal Source Symbols Differ from Real Hardware

Ideal sources do not exist because a real supply has finite internal resistance, so it behaves as a voltage source until the current demand becomes large enough that the internal drop dominates. That crossover is exactly what a bench supply is showing you when it switches from CV to CC.

The arrow direction on a current source is not decoration. It defines the reference direction for the current, and a solution that returns a negative value simply means that the real current flows in the opposite direction.

Dependent (Controlled) Source Symbols

Figure: The four dependent source symbols

A dependent source, also called a controlled source, produces an output that is controlled by a voltage or current elsewhere in the circuit.

It is typically drawn as a diamond rather than a circle. The diamond distinguishes a dependent source from an independent source, while the internal markings indicate whether it is a voltage or current source.

The Four Dependent Source Types

The controlling quantity is always named on the schematic, usually as a labeled branch current or a labeled node voltage elsewhere on the sheet. Without that label, the symbol is unusable, because nothing tells you what the output follows.

Where Dependent Source Symbols Appear in Real Circuits

Dependent sources are not a textbook abstraction. They are how every active device is modeled:

• A bipolar transistor in its small-signal model is a CCCS, with collector current following base current.
• A MOSFET is a VCCS, with drain current following gate-source voltage.
• An ideal op-amp is a VCVS, with the output following the differential input.
• A transimpedance amplifier can be modeled as a CCVS, converting an input current into an output voltage.

Unlike the earth mark, which is numbered in IEC 60417, the diamond is not a numbered entry in IEC 60617, but it is almost universally used as a drafting convention.

It's been used throughout circuit theory books, in SPICE and later circuit simulators, and in EDA libraries, so use it as the de facto standard of practice, but don't quote a clause number for it that does not exist.

For the op-amp case, our op-amp symbol guide covers how the supply pins are drawn and why they are often hidden.

Power Rail Labels: VCC, VDD, VSS, VEE, and GND

Rail labels are power supply symbols in text form. A short stem with an upward bar or arrow, carrying a name, declares a supply net without drawing a wire all the way back to the source.

VCC vs VDD: Which Label Should You Use?

In modern practice, VCC and VDD are used interchangeably for the positive rail, and VSS and GND are used interchangeably for the return. The distinction survives from device physics rather than from any current standard.

Historically, when transistors (BJT) are used, the supplies have to power the collector, hence named VCC. Now CMOS is everywhere. The drain is powered by the supplies; hence, VDD is named.

In modern practice, while label selection often reflects design conventions, the best practice is always to follow the power-pin names in the component datasheet.

Power Supply Symbols: IEC 60617 vs ANSI/IEEE 315

Figure: IEC 60617 and ANSI/IEEE 315 electrical symbol comparison

IEC 60617 governs graphical symbols for diagrams internationally, and ANSI/IEEE 315 is the North American equivalent.

The resistor row is included because it is where engineers first notice the two standards diverge. For power sources specifically, however, a schematic drawn to either standard remains fully understandable to engineers trained in the other.

How to Read Power Supply Symbols in a Circuit

Read power symbols in a fixed order, and a schematic resolves quickly. Work from the source down to the return, then check the references.

Figure: A worked example schematic showing a supply rail, decoupling, a dependent source, and the ground return path.

1. Find the source and identify its family. Circle for independent, diamond for dependent, bar pairs for a battery. The outline answers this before you read any label.
2. Read the contents for type and direction. Polarity marks mean a voltage source, an arrow means a current source, and a sine wave means AC.
3. Trace the positive rail across the sheet. Collect every rail label that matches, since they are the same net whether or not a wire joins them.
4. Identify every ground glyph separately. Count how many distinct return symbols appear. Two different symbols mean two different nets.
5. Locate the tie point. Find where the separate returns meet, usually a single net tie or zero-ohm link. If you cannot find one, the schematic has a defect.
6. Check the controlling variable on any diamond. A dependent source without a named control is incomplete.

Common Power Supply Symbol Mistakes

Most power symbol errors are drafting errors that survive review because the schematic still looks plausible.

• Drawing a dependent source as a circle: this is the single most common error, and it makes a controlled source read as an independent supply. Simulation then converges on a completely wrong operating point.
• Tying chassis ground to earth ground implicitly: placing both symbols on the same net without an explicit bond creates a ground loop that shows up as a failed EMC scan, not as a DRC error.
• Equal-length battery bars: the polarity becomes ambiguous, and a reversed cell holder on the board follows.
• Unlabelled AC sources: an AC symbol without RMS voltage and frequency cannot be built or simulated.
• Using IEC 60417 equipment marks on a schematic: the line-and-dash DC mark belongs on a rating plate, not in a netlist.
• Reusing GND for analog and power returns: one net name collapses two returns that needed separating, and the switching noise ends up in your reference.

From Power Supply Symbol to PCB Footprint

A power symbol only becomes a physical connection when it acquires a footprint, a net class, and copper. This is the step where schematic decisions turn into manufacturable ones.

Figure: A workflow strip tracing one power supply symbol

Trace Width and Net Class for Power Nets

Trace width is where the power net stops being a symbol. Under IPC-2221, the required width is a function of three things:

• Current: the continuous current the net carries, not the peak.
• Acceptable temperature rise: typically 10 C to 20 C above ambient.
• Layer position: internal or external.

Internal layers need significantly more width than external layers for the same current, because buried copper dissipates heat poorly. A 2 A rail on a 1 oz outer layer is a very different trace from the same rail buried on an inner layer.

Set the net class in your EDA tool at the same time you place the power symbol. That way, the width rule automatically follows the net rather than being remembered at routing time.

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Conclusion

Power supply symbols are a small vocabulary that does a large amount of work. Four families cover almost everything: circles for independent sources, diamonds for dependent ones, bar pairs for batteries, and three distinct symbols for the returns. The shapes are stable across IEC 60617 and ANSI/IEEE 315, so once you can read one convention, you can read both.

The two mistakes worth guarding against are drawing a controlled source as a circle and treating the chassis, earth, and signal ground as a single net. Neither triggers a design rule check, and both are expensive to find after fabrication. Get the symbols right on the schematic and the net classes, plane assignments, and trace widths follow naturally.

FAQs About Power Supply Symbols