A capacitor is a capacitor — until you notice that two capacitors with the same capacitance value behave completely differently in a circuit. The type determines not only how much charge a capacitor stores, but also how fast, how stable, and under what conditions it does so.
The three most commonly used types
Electrolytic capacitors
An electrolytic capacitor is polarized — if you connect it backward, it can get damaged or even explode. It is suitable for high capacitance values (µF to thousands of µF) at a low cost. You can find them in power supplies as smoothing/buffer capacitors and in audio circuits.
Limitations: limited lifespan at high temperatures, relatively high ESR, and unsuitable for AC voltage.
Ceramic capacitors (MLCC)
Small, cheap, and non-polarized. Low ESR, suitable for high frequencies — the standard choice for decoupling right next to ICs. Pay attention to the X7R/X5R specification: the capacitance drops sharply at higher voltages (DC bias effect).
Film capacitors
Non-polarized, low leakage current, stable capacitance value across temperature and frequency. The PME271 from Kemet is an X2 capacitor — certified for use in circuits directly connected to mains voltage.
When do you choose which type?
| Application | Recommended type |
|---|---|
| Power supply buffering, large capacitance | Electrolytic |
| Decoupling at ICs | Ceramic (100 nF, close to the IC) |
| Filtering applications, audio | Film (low distortion, stable) |
| EMI suppression on mains voltage | X2 film capacitor (PME271) |
| High frequency, RF | Ceramic (NP0/C0G) |
The PME271 in practice
The PME271 is X2-certified for use on mains voltage. You can find it in noise suppression circuits in switching power supplies, filter stages, and EMC suppression. If it fails, it does so in a safe manner (fail-safe).
Practical points to watch out for
- Choose a voltage rating with a margin. Aim for a factor of 1.5 to 2 above the maximum voltage in the circuit.
- ESR matters in power supplies. Use low-ESR capacitors in switching power supplies.
- Check the temperature class. Electrolytic capacitors come in 85°C and 105°C variants. In hot environments, always choose the 105°C variant.
- Check the polarity. The white stripe on an electrolytic capacitor indicates the negative terminal. Film and ceramic capacitors are non-polarized.
