If you're using any electronic device now, you're likely using a capacitor without knowing. This critical component is useful as far as the storage of charge is concerned.
Understanding capacitor symbols is essential for reading schematics and designing circuits. Different capacitor types use different symbols to convey important information about polarity and adjustability.
Standard Non-Polarized Symbol
The basic capacitor symbol consists of two parallel lines representing the capacitor plates. Both lines are straight and equal length, indicating the capacitor can be connected in either direction.
This symbol is used for:
- Ceramic capacitors
- Film capacitors (polyester, polypropylene)
- Mica capacitors
- Glass capacitors
Polarized Capacitor Symbol
Polarized capacitors use a modified symbol with one curved plate:
- Straight line = Positive terminal (+)
- Curved line = Negative terminal (-)
This symbol indicates the capacitor must be connected with correct polarity. Used for:
- Aluminum electrolytic capacitors
- Tantalum capacitors
- Supercapacitors
Variable Capacitor Symbol
Variable (adjustable) capacitors include an arrow through the symbol, indicating the capacitance can be changed. Used for:
- Trimmer capacitors
- Tuning capacitors
- Varactors (voltage-variable)
Regional Variations
IEC/European Style: Uses two parallel rectangles instead of lines.
US/ANSI Style: Uses the line-based symbols described above.
Most modern schematics use US style, but you may encounter European symbols in international documents.
Schematic Designators
Capacitors are labeled with reference designators starting with C:
- C1, C2, C3, etc.
- Sometimes EC for electrolytic, CV for variable
Capacitance Values and Units
Capacitance is measured in Farads (F), but practical values are much smaller:
| Unit | Symbol | Relation |
|---|---|---|
| Farad | F | 1 F |
| Millifarad | mF | 0.001 F |
| Microfarad | µF | 0.000001 F |
| Nanofarad | nF | 10⁻⁹ F |
| Picofarad | pF | 10⁻¹² F |
Capacitor Code System
Many capacitors use a 3-digit code:
- First two digits: significant figures
- Third digit: number of zeros (multiplier in pF)
Examples:
- 104 = 10 + 0000 = 100,000 pF = 100 nF = 0.1 µF
- 473 = 47 + 000 = 47,000 pF = 47 nF
- 102 = 10 + 00 = 1,000 pF = 1 nF
Tolerance Codes
Letters indicate tolerance:
| Code | Tolerance |
|---|---|
| J | ±5% |
| K | ±10% |
| M | ±20% |
| D | ±0.5% |
| F | ±1% |
Voltage Ratings
Schematics often show voltage rating:
- 10µF/25V or 10µF 25V
- Always use capacitors rated above your circuit voltage
Reading Schematics
When reviewing schematics:
- Identify symbol type (polarized vs non-polarized)
- Note reference designator (C1, C2)
- Find value near symbol or in parts list
- Check voltage rating if shown
- Verify polarity for polarized types
Common Mistakes
- Confusing µF with nF (1000x difference)
- Ignoring polarity on electrolytic capacitors
- Using wrong voltage rating
- Misreading 3-digit codes
Conclusion
Capacitor symbols indicate type and polarity. Non-polarized capacitors show two equal lines; polarized types have one curved line (negative). Values use codes or direct notation in pF, nF, or µF. Always verify polarity when using electrolytic or tantalum capacitors.
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