C5. Variable Capacitors Variable capacitors are used for trimming and tuning purposes. They represent a small but important part of the capacitor assortment. C 5.1. GENERAL DESCRIPTION By means of an electrode system consisting of one fixed and one movable part – stator and rotor – the capacitance can be varied between a minimum and a maximum value, the so called capacitance swing. The...

C 4.4. The time constant, t The time constant of electrostatic capacitors is defined in section C1.2.2 as the time needed to discharge a loaded capacitor through the insulation resistance (IR) to 1/e (~37%) of the initial voltage. This constant denominated t(tau) is the product of IR and C (capacitance), usually abbreviated RC.  As already mentioned, supercapacitors don’t have any dielectric even if the...

C 4.0 SUPERCAPACITORS C 4.1. Introduction and Basic Function Supercapacitors (or ultracapacitors) are the fastest growing capacitor technology on the market offering very high DC capacitance and high energy densities. Sometimes all supercapacitors are mis-called as EDLC (Electric Double Layer Capacitors), but as we will explain shortly, EDLC is large, but only one part of supercapacitor family. Supercapacitors features sit between capacitors and batteries,...

C 3.8  WET TANTALUM ELECTROLYTICS C 3.8.1.                 Introduction Wet tantalum capacitors have several advantages over solid tantalum, aluminum electrolytic, and ceramic capacitors. As with all other capacitors, these advantages lead to a very specific “sweet spot” or focused area of applications where the wet tantalum capacitor is the best and preferred choice. Wet tantalums require little derating and offer higher voltages (75 V,...

C 3.7. SOLID NIOBIUM and NIOBIUM OXIDE CAPACITORS Niobium is a sister metal to tantalum, and shares many chemical characteristics with it, in addition to a few disadvantages and advantages of its own when used as a capacitor dielectric. Niobium capacitor technology has existed for decades, but its limitation in maximum rated voltage, lower volumetric efficiency, incompatibility with low ESR polymer electrode, limited range...