What Is a Film Capacitor?
A film capacitor is a non-polarized, very stable and low-loss capacitor that uses a thin plastic film as the dielectric.
Operation and Structure
Plastic film layers are wound with a metal coating. This structure gives a stable capacitance that changes very little with time and temperature.
Types
| Type | Code | Property |
|---|---|---|
| Polyester | MKT | Cheap, general purpose |
| Polypropylene | MKP | Low loss, high quality |
Advantages
High stability, low ESR, low loss and a self-healing property. It withstands AC and high voltage.
Where Is It Used?
Preferred in audio circuits, AC applications, motor starting, snubbers and filter circuits.
Self-Healing
Film capacitors have an important property: if a small puncture occurs in the dielectric, the thin metal coating there vaporizes and isolates the faulty spot. This self-healing behavior makes them long-lived and reliable in AC-mains and high-voltage applications.
Common Mistakes
- Confusing the AC rating: in AC applications a suitable X/Y-class film capacitor must be chosen.
- Underestimating the size: at the same capacitance it's larger than ceramic; plan the space.
- Expecting high capacitance: film capacitors are usually in the low-to-medium capacitance range.
Frequently Asked Questions
What's the difference between MKT and MKP?+
Does a film capacitor have polarity?+
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