What Is Capacitance?
Capacitance is the ability of a capacitor to store electrical charge. It is defined as the amount of electric charge (Q) stored per unit of voltage (V) across its plates:
Where:
C= Capacitance (in farads, F)Q= Charge (in coulombs)V= Voltage (in volts)
Common Capacitance Units
Because 1 farad is a very large value, most practical capacitors are measured in:
- Microfarads (µF) = 10⁻⁶ F
- Nanofarads (nF) = 10⁻⁹ F
- Picofarads (pF) = 10⁻¹² F
Factors That Affect Capacitance
- Plate Area: Larger plates = more capacitance.
- Distance Between Plates: Smaller gap = more capacitance.
- Dielectric Material: Different materials affect how well the capacitor stores charge.
What Is Capacitor Tolerance?
Tolerance indicates how much the actual capacitance value can vary from its labeled value.
Example:
A 100 µF capacitor with ±10% tolerance could actually be anywhere between 90 µF and 110 µF.
Common Tolerance Codes:
- ±5%: J
- ±10%: K
- ±20%: M
High-precision applications (like timing circuits) require tight tolerance capacitors, while general-purpose filters can use looser tolerances.
What Is Voltage Rating?
The voltage rating of a capacitor is the maximum voltage it can handle safely without breaking down or becoming damaged.
Key Points:
- Exceeding the rated voltage can cause leakage, short circuit, or explosion.
- Always choose a capacitor with a higher voltage rating than your circuit requires.
Example:
- A capacitor rated at 25V should not be used in a circuit that will expose it to 30V.
- For a 12V circuit, using a capacitor rated for 16V or 25V is a good practice.