Variable capacitor basics
As we know capacitors are of two types viz. fixed capacitor and variable capacitor. Fixed capacitor will provide fixed capacitance in the electronic circuit. Variable capacitor will provide varying capacitance as required in the circuit. It is used to tune the radio receiver to the desired frequency.
Variable capacitor is composed of two sets of metal plates parallel to each other. One plate is fixed and the other plate moves on a spindle within the fixed set. Both of these plates are separated by dielectric either air or some solid material.
For some applications two or more air spaced type capacitors are ganged. Due to this capacitance in the several circuits is changed together when the spindle is rotated. The maximum capacitance achieved with fully overlapped plates is about 500pF.
Trimmers and preset capacitors are used as variable capacitors for many applications. There are mica capacitors of compression type in which mica sheets are compressed more or less by tuning a screw. This results into change in capacitance.
Variable capacitor manufacturers
Following are few of the reputed variable capacitor manufacturers:
1. muRATA
2. Vishay
3. Voltronics Corporation
4. Johanson manufacturing corporation
5. Mouser electronics
6. ECI
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