Variable capacitors can be divided into air dielectric variable capacitors and solid dielectric variable capacitors according to the dielectric materials they use.

Variable capacitor, referred to as "variable / adjustable capacitor", is a capacitor whose capacitance can be adjusted within a certain range. Common variable capacitors include air single connected variable capacitors, air double connected variable capacitors, small sealed single connected variable capacitors, small sealed double connected variable capacitors, ceramic trimmer capacitors, Line fine-tuning capacitors, etc. Now let's learn about the structure, characteristics and specific applications of variable capacitors.

The variable capacitor is composed of a group of fixed pieces and a group of moving pieces, and its capacity can be continuously changed with the rotation of the moving pieces. Two groups of variable capacitors are installed together and rotate coaxially, which is called double connection. The medium of variable capacitance includes air and polystyrene. The air medium variable capacitor is large in volume and small in loss, which is often used in electronic tube radios. The polystyrene dielectric variable capacitor is made into a sealed type, which is small in size and is mostly used in transistor radios.

Structure. The variable capacitor has two groups of mutually insulated metal sheets to form electrodes: one group is fixed (fixed piece), and the other group is installed on the rotating shaft and can rotate (moving piece). The fixed piece and moving piece leading out end of solid sealed single and double connected variable capacitors and air single and double connected variable capacitors shall not be wrongly connected in use. Double connected variable capacitors generally have only one moving blade outlet, which is shared by two connections.

So, what are the characteristics of variable capacitors?

It is often used in the tuning circuit of radio to select radio stations.

The characteristic of the capacitance is that the capacitance can be changed, and the rotation angle of the moving plate is usually 180 °?, The capacity is large when all the moving pieces are screwed into the fixed pieces, and small when all the moving pieces are screwed out. According to the characteristics of the change of the rotating angle of the capacity follower, the variable capacitor can be divided into linear capacitance type, linear frequency type, logarithmic type, etc.

The capacitor should be applied to the oscillator to make the oscillation frequency continuously adjustable within a certain range. In the high-frequency signal generator circuit, adjust the single love variable capacitor C, and its output signal frequency can be changed as needed.