What Is an Electrolytic Capacitor?

An electrolytic capacitor is a polarized component that packs large capacitance into a small package. It uses a conductive electrolyte as one electrode, which enables an extremely thin dielectric layer and high capacitance density.

How It Works

The capacitor has four layers:

• Anode foil: High-purity aluminum, electrochemically etched for maximum surface area
• Dielectric: A microscopically thin aluminum oxide layer formed by anodization
• Electrolyte: Conductive liquid, gel, or solid polymer acting as the cathode
• Cathode foil: Aluminum foil connecting to the electrolyte

These layers are wound into a cylinder and sealed in an aluminum can. The thin oxide dielectric blocks DC current while allowing the electrostatic field to store charge. This thinness is what gives electrolytics their high capacitance-to-volume ratio — and why they are polarized.

Types of Electrolytic Capacitors

Aluminum Electrolytic

The most common type. Uses liquid or solid electrolyte with aluminum foil electrodes. Available as SMD, radial, snap-in, and screw-terminal.

Tantalum Electrolytic

Uses tantalum metal anode with manganese dioxide or polymer electrolyte. More stable over temperature. Common in smartphones and medical devices.

Solid Polymer

Replaces liquid electrolyte with conductive polymer. Lower ESR, longer life, better high-frequency performance. Used in motherboards and GPU cards.

Hybrid Polymer

Combines liquid electrolyte with solid polymer. Low ESR plus high capacitance. Popular in automotive and industrial applications.

Key Specifications

• Capacitance tolerance: Typically +/-20% for aluminum electrolytics
• ESR: Internal resistance generating heat under ripple current. Lower is better
• Ripple current rating: Maximum AC current before overheating. Often the limiting factor in power supply designs
• Operating life: A capacitor rated 2,000 hours at 105 C lasts about 16,000 hours at 75 C

Quick Selection

1. Power supply: Aluminum electrolytic, snap-in or radial, 105 C rated
2. Portable device: Tantalum or solid polymer, SMD
3. High-frequency: Solid polymer or hybrid, low ESR critical
4. High-temperature: 125 C rated, verify lifetime calculation

Key Takeaways

• Electrolytic capacitors give the most microfarads per dollar and per cubic centimeter
• They are polarized — always observe correct polarity
• Temperature and ripple current determine lifetime
• Solid polymer types offer lower ESR and longer life than traditional wet electrolytics

Need electrolytic capacitors? Contact Xuansn for samples and datasheets.