Let's talk about the absorption coefficient of film capacitors

Film capacitors are ubiquitous in our lives, with wide applications such as in common appliances like air conditioners, refrigerators, washing machines, and water heaters. Today, we'll explore film capacitors, including their absorption coefficient, its function, and any abnormal situations that might occur. Let's learn together!

A film capacitor is a type of capacitor that uses metal foil as electrodes, overlapped at both ends with plastic films such as polyethylene, polypropylene, polystyrene, or polycarbonate, and then wound into a cylindrical shape. Polypropylene film capacitors are characterized by their very low absorption coefficient, minimal change in capacitance and loss tangent (tg σ) with temperature, and a slight increase in dielectric strength with increasing temperature—features rarely found in other capacitors. What is the absorption coefficient? It's a numerical value describing the dielectric absorption phenomenon in a film capacitor, related to the dielectric, dielectric polarization, and the capacitor's absorption behavior. This coefficient is not uniform; it varies between different manufacturers, different models, and batches, and even individual film capacitors from the same manufacturer and batch may differ.

The dielectric absorption effect of a film capacitor determines its low-frequency characteristics. A smaller absorption coefficient results in a better film capacitor, leading to faster charging and discharging. Ideally, if the absorption coefficient were zero, the dielectric (i.e., the insulator) would exhibit no polarization under an applied electric field, the dielectric surface would have no force binding charges, and the capacitor's charging and discharging response would be lag-free. However, this is an ideal scenario and cannot be achieved with current technology.

If the absorption coefficient is too large, the capacitor's charging and discharging response will be severely delayed, the time constant of the ultra-low frequency smoothing filter will increase, the DC amplifier's zero point will be disturbed, resulting in unidirectional drift, increased power supply circuit ripple, and so on. Therefore, the absorption coefficient of the thin film capacitor should be as small as possible.

After reading this article, you should have a better understanding of the absorption coefficient of film capacitors. If you have any technical questions, please contact us, and we will be happy to answer them for you.