Complete Guide to Capacitors
Learn everything about capacitors: types, formulas, charging and discharging, applications, and practical usage in electronics projects and circuits.
What is a Capacitor?
A capacitor is a passive electrical component that stores energy in the form of an electric field. It consists of two conductive plates separated by an insulating material called a dielectric. Capacitors are used for energy storage, filtering, coupling signals, timing applications, and more.
- Unit: Farad (F)
- Symbol in schematics:
C - Charge stored:
Q = C × V - Voltage across capacitor:
V = Q / C
Capacitor Types
Capacitors come in various types, each with specific characteristics:
- Ceramic Capacitors: Non-polarized, small values, common in decoupling applications.
- Electrolytic Capacitors: Polarized, larger capacitance, used for bulk energy storage.
- Tantalum Capacitors: Stable and reliable, often used in precision electronics.
- Film Capacitors: Non-polarized, stable, used in high-frequency circuits.
- Supercapacitors: Very high capacitance, store large amounts of energy for short-term applications.
Capacitance and Voltage Ratings
The capacitance value indicates how much charge the capacitor can store at a given voltage. Voltage ratings must not be exceeded:
// Example: 100µF, 16V
C = 100µF
Vmax = 16V
Qmax = C × V = 100 × 10^-6 × 16 = 0.0016 C
Capacitor Charging and Discharging
Capacitors charge through a resistor according to the exponential formula:
Charging: V(t) = Vmax × (1 - e^(-t / (R×C)))
Discharging: V(t) = V0 × e^(-t / (R×C))
Time constant τ = R × C
Where τ (tau) is the time constant determining how fast the capacitor charges or discharges.
Applications of Capacitors
Capacitors have a wide range of applications:
- Decoupling power supply lines to reduce noise
- Coupling AC signals between stages
- Timing and oscillator circuits
- Energy storage for cameras, flash devices, or supercapacitors in renewable energy
- Filter circuits in power supplies to smooth voltage
Practical Examples
Using a capacitor in a simple LED blinking circuit:
// RC Blinking LED
R = 10kΩ
C = 100µF
Time Constant τ = R×C = 10,000 × 100×10^-6 = 1 sec
LED flashes at ~1Hz depending on R and C values
Using a capacitor to filter DC in a power supply:
// Capacitor Filter
Input AC → Rectifier → Capacitor → DC Output
C smooths ripples, improves stability
Typical: 1000µF / 25V for small power supplies
Advanced Concepts
- Dielectric Types: Influence capacitance stability, frequency response, and leakage.
- ESR (Equivalent Series Resistance): Important in power applications, affects ripple voltage.
- Polarized vs Non-Polarized: Polarized capacitors must respect correct voltage polarity.
- AC vs DC Applications: Some capacitors block DC but pass AC, e.g., coupling capacitors.
- Energy Storage: E = ½ × C × V²
// Energy Stored in Capacitor
C = 100µF, V = 12V
E = 0.5 × 100×10^-6 × 12² = 0.0072 Joules
Capacitor Circuits
Series: 1/C_total = 1/C1 + 1/C2 + ...
Voltage divides among capacitors inversely proportional to capacitance.
C1 = 100µF, C2 = 200µF
1/C_total = 1/100 + 1/200 = 0.015
C_total = 66.67µF
Parallel: C_total = C1 + C2 + ...
C1 = 100µF, C2 = 200µF
C_total = 100 + 200 = 300µF
Filter capacitors smooth out voltage in power supplies; decoupling capacitors suppress noise near ICs.
Capacitors determine frequency in LC and RC oscillators.
Supercapacitors store large energy for backup systems or energy harvesting circuits. Charge/discharge rapidly, often replacing batteries in small circuits.
Capacitor Types Quick Reference
Non-polarized
Polarized
Polarized
Non-polarized
High Capacitance
Multi-layer Ceramic
Trimmer Capacitor
Choosing Capacitors for Projects
0.01µF–0.1µF Ceramic
100µF–4700µF Electrolytic
10nF–100µF Film or Electrolytic