Variable Capacitors

Trimmer capacitors, called just trimmers for short, belong to the passive components in this category. That means their capacitance is mechanically steplessly adjustable within defined limits. They consist of two semi-circular plate packages, with an insulating layer, the dielectric, of air or plastic. One of the two plate packages of the trimmer can be adjusted by turning a screw ­– with rotary capacitors the difference is that a shaft is turned – completely into or out of the plate package. The range of capacitance adjustment available by a rotation of 180° is generally merely of the order a few 10 pF (picofarad). Probably the best-known field of application of rotary capacitors used to be in broadcasting technology. Here they were used with control knobs for transmitter adjustment. Trimmer capacitors are generally used to adjust or fine tune the capacitance in circuits.