Surface-mount capacitors are so small that their values are printed in cryptic 3-digit codes. Meanwhile, choosing the right capacitance for a filter circuit requires understanding frequency response, impedance, and real-world capacitor behavior.
Reading SMD Capacitor Codes
Most ceramic capacitors use a 3-digit code: first two digits are the value, third digit is the multiplier in picofarads (pF).
- 104 = 10 × 10⁴ pF = 100,000 pF = 100 nF = 0.1 µF
- 103 = 10 × 10³ pF = 10,000 pF = 10 nF
- 472 = 47 × 10² pF = 4,700 pF = 4.7 nF
- 226 = 22 × 10⁶ pF = 22,000,000 pF = 22 µF
Some manufacturers use a letter+digit system: "µ1" = 0.1 µF, "10" = 10 pF. Check the datasheet if unsure.
Capacitor Types and Applications
Ceramic (MLCC): 1 pF – 100 µF. Fast, cheap, low ESR. Used for decoupling, filtering, and coupling. X7R and X5R are general-purpose; C0G/NP0 for precision.
Electrolytic: 0.1 µF – 10,000 µF. Polarized, higher ESR. Used for bulk power supply filtering. Must be installed with correct polarity.
Tantalum: 0.1 µF – 1,000 µF. Compact, stable, polarized. Used in space-constrained designs. Can fail short-circuit if overvoltaged.
Filter Circuit Design
A simple RC low-pass filter: f_cutoff = 1 ÷ (2π × R × C). For a 1 kHz audio filter with R = 10 kΩ: C = 1 ÷ (2π × 10,000 × 1,000) = 15.9 nF → use 15 nF or 16 nF standard value.
Power supply decoupling: place a 100 nF ceramic capacitor as close as possible to each IC's power pin. Add a 10 µF bulk capacitor for each section of the PCB. This covers a wide frequency range.
Try the Electric Capacitance Converter
Convert between all electric capacitance units instantly.