Electrolytic Capacitor Symbol
Definition: The Electrolytic Capacitor symbol represents a polarised capacitor that uses an electrolyte to achieve high capacitance in a compact package, depicted in IEC 60617 as two parallel lines with a curved negative plate and a '+' polarity marker on the positive terminal, and in ANSI Y32.2 / IEEE 315 as two parallel lines with a '+' sign beside the positive plate, with designator C and capacitance measured in farads (F).
Also known as: electrolytic cap, polarised capacitor, electrolytic, aluminium electrolytic capacitor, e-cap, polarized capacitor.
What the Electrolytic Capacitor symbol means
The Electrolytic Capacitor symbol denotes a polarised capacitor in which an aluminium oxide layer formed on the anode foil acts as the dielectric, enabling very high capacitance values (1 µF to tens of thousands of µF) in a cylindrical can package. The polarity markings — '+' on the positive terminal and '−' on the negative terminal — are critical: reversing the applied voltage will damage or destroy the capacitor and may cause it to vent or rupture.
In circuit schematics, the electrolytic capacitor symbol with its polarity markers tells the designer and assembler which pin connects to the higher potential. This symbol is used wherever bulk energy storage, supply decoupling, or low-frequency filtering is required, particularly in power supplies, audio amplifiers, and motor-drive circuits.
How to identify the Electrolytic Capacitor symbol
The electrolytic capacitor symbol consists of two horizontal lines (the capacitor plates). The positive plate is drawn as a straight solid line; the negative plate is drawn as a curved line (IEC 60617) or a straight line with a minus sign (ANSI/IEEE 315). A '+' symbol appears beside the positive (upper or left) plate. The two pins are labelled '+' (positive, anode) and '−' (negative, cathode). This polarity indication clearly distinguishes it from a non-polarised capacitor symbol, which has two straight parallel lines of equal style with no polarity markers.
Function in a circuit
An electrolytic capacitor stores electrical charge on the aluminium-oxide dielectric layer between the anode foil and electrolyte, delivering it back when circuit voltage drops. In power supply filters it smooths rectified DC by charging during voltage peaks and discharging during troughs, reducing ripple voltage. In audio and signal circuits it blocks DC while coupling AC signals between stages. In motor-start circuits a large electrolytic capacitor provides the phase-shifted current needed to start single-phase induction motors.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-04 (passive components) defines the polarised capacitor symbol: a straight line for the positive plate and a curved line for the negative plate, with a '+' marker beside the positive terminal. IEC 60384-4 specifies performance requirements for aluminium electrolytic capacitors. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2-1975 (R1989) / IEEE 315-1975 shows the polarised capacitor as two parallel lines — both straight — with a '+' sign beside the positive plate and, in some versions, a '−' beside the negative plate. The curved-plate convention is an IEC distinction. |
| Key difference | IEC 60617 uses a curved negative plate to visually signal polarity; ANSI/IEEE 315 uses two straight plates but includes explicit '+' and '−' polarity labels. Both standards agree that the positive terminal must be clearly marked. |
Terminals / pins
| Pin | Name |
|---|---|
| pos | + |
| neg | - |
Typical values
Capacitance range: 1 µF to 100,000 µF (100 mF). Voltage rating (WVDC): 6.3 V to 450 V DC (standard series). Ripple current rating: typically 0.1 A to several amperes depending on size. Temperature range: −40 °C to +105 °C (high-temp series). ESR (equivalent series resistance): 10 mΩ to several ohms depending on capacitance and frequency.
Where the Electrolytic Capacitor symbol is used
- Linear and switched-mode power supply output filters: large electrolytics (470 µF–10,000 µF, 10–50 V) reduce output ripple to acceptable levels
- Audio amplifier power supply decoupling and coupling capacitors: 100 µF–1000 µF for supply bypass; 10–100 µF for inter-stage DC-blocking
- Motor-start and motor-run circuits: 50–400 µF electrolytic motor-start capacitors provide the phase shift required by single-phase induction motors
- Voltage-doubler and charge-pump circuits where back-to-back electrolytics store and transfer charge at low frequencies
- Timing circuits: RC time constants using electrolytic capacitors for seconds-to-minutes delays (e.g., relay time-delay modules)
- Switching regulator input capacitors to handle large AC ripple current from the switching action of SMPS topologies
Example
In a 12 V / 2 A linear bench power supply, a 2200 µF 25 V electrolytic capacitor is connected between the rectifier bridge output and ground; the '+' pin connects to the positive DC rail and the '−' pin to the ground rail. The capacitor charges to the rectifier peak voltage and discharges into the regulator during the mains zero-crossings, reducing output ripple from several volts to less than 100 mV peak-to-peak.
Key facts
- The Electrolytic Capacitor symbol is a polarised capacitor symbol with a '+' marker on the positive terminal (anode) and a curved negative plate in IEC 60617 notation; reversing polarity even briefly can destroy the device.
- The positive pin is labelled '+' (pin id: pos) and the negative pin is labelled '−' (pin id: neg); the '+' pin must always connect to the more positive voltage node in the circuit.
- Electrolytic capacitors use an aluminium-oxide dielectric layer (formed by anodisation) that is only a few nanometres thick, enabling capacitance densities far higher than film or ceramic capacitors of the same physical volume.
- IEC 60617-04 draws the electrolytic capacitor with a curved negative plate; ANSI Y32.2 / IEEE 315 uses two straight plates with explicit polarity labels — this is the primary visual difference between the two standards.
- Designator letter: C (e.g., C1, C2). Capacitance is measured in farads (F); practical values are expressed in microfarads (µF) or millifarads (mF). The component has 2 terminals: positive (+) and negative (−).
- Electrolytic capacitors have a finite operational lifetime determined by electrolyte evaporation; rated lifetime is typically 1,000–10,000 hours at maximum temperature. Exceeding the working voltage (WVDC) or reverse-biasing will rapidly degrade the oxide layer.
- IEC 60384-4 distinguishes plain aluminium electrolytics from solid-electrolyte types (polymer capacitors); polymer electrolytics have lower ESR and longer life but are limited to lower voltage ratings (typically ≤100 V).
Frequently asked questions
What does the electrolytic capacitor symbol look like?
The electrolytic capacitor symbol shows two horizontal lines representing the capacitor plates. In IEC notation the positive plate is a straight line and the negative plate is a curved line, with a '+' marker beside the positive plate. In ANSI/IEEE notation both plates are straight lines with '+' and '−' labels beside the appropriate plate.
What does the electrolytic capacitor symbol mean in a circuit?
The electrolytic capacitor symbol represents a polarised, high-capacitance energy-storage component. The '+' and '−' markings indicate which terminal connects to the higher and lower voltage respectively. Installing the capacitor with reversed polarity will damage it and may cause violent failure.
What is the difference between the IEC and ANSI electrolytic capacitor symbols?
IEC 60617-04 draws the negative plate as a curved line to signal polarity visually; ANSI Y32.2 / IEEE 315 uses two straight parallel lines with explicit '+' and '−' polarity labels beside the plates. Both standards require clear polarity marking, but the curved plate is a distinctly IEC visual convention.
How do I identify the positive and negative pins of an electrolytic capacitor symbol?
The positive pin is marked with a '+' symbol beside the plate and is labelled '+' (pin id: pos) in schematic netlist notation. The negative pin is marked '−' and is labelled '−' (pin id: neg). On a physical component, the negative lead is identified by a stripe with minus signs on the capacitor body.
What is the designator letter for an electrolytic capacitor?
The designator letter is C (for capacitor), for example C1, C4, C12. The unit of capacitance is the farad (F); electrolytic capacitors are typically specified in microfarads (µF). On schematics, the value and voltage rating are written beside the designator, e.g. C3 2200 µF / 25 V.
What standard governs electrolytic capacitor symbols?
Electrolytic capacitor symbols are defined in IEC 60617-04 (graphical symbols for diagrams — passive components) for IEC-standard drawings, and in ANSI Y32.2-1975 (R1989) / IEEE 315-1975 for North American drawings. Performance requirements for aluminium electrolytic capacitors are specified in IEC 60384-4.
What are the typical capacitance values of electrolytic capacitors?
Electrolytic capacitors range from about 1 µF to 100,000 µF (100 mF). Voltage ratings span 6.3 V to 450 V DC. Common power-supply filter values are 470 µF to 10,000 µF at 16–63 V. Smaller values (1–100 µF) are used for decoupling and audio coupling applications.
Can an electrolytic capacitor be used in AC circuits?
Standard aluminium electrolytic capacitors are polarised and cannot be directly connected to AC voltage because the voltage reversal will damage the oxide dielectric. In AC applications, two electrolytic capacitors are connected back-to-back (series, anti-series) to form a non-polarised combination, or a non-polarised electrolytic (NP type) rated for bipolar use is specified.
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