Variable capacitors are capacitors whose capacitance can be adjusted within a certain range. Variable capacitors can be divided into fine-tuning variable capacitors, single-connected variable capacitors, double-connected variable capacitors, and quad-connected variable capacitors according to different structures.

1 Trimming variable capacitor

Fine-tuning variable capacitors are also called semi-adjustable capacitors, and the adjustable range of capacitance is small.

Trimming variable capacitors mainly include ceramic trimming variable capacitors, wire trimming variable capacitors, mica trimming variable capacitors, film trimming variable capacitors, etc.

The capacitance of the fine-tuning variable capacitor is generally 5 ~ 45pF, and the adjustable range is small. It is mainly used in the tuning circuit of the radio.

Variable capacitors are generally composed of two sets of pole pieces that are insulated from each other. Among them, a group of fixed pole pieces is called a fixed piece; a group of movable pole pieces is called a moving piece. The variable capacitor can change the capacitance correspondingly by changing the relative effective area or distance between the pole pieces, and is mainly used for selecting signals (tuning) in radio receiving circuits.

2 Single-connected variable capacitors

A single-connected variable capacitor is composed of two sets of metal aluminum sheets that are insulated from each other. This type of capacitor has only one adjustable capacitor inside.

Adjusting the shaft of the single-connected variable capacitor can drive its internal moving piece to rotate, thereby changing the relative position of the stator and the moving piece, so that the capacitance changes accordingly.

The pins of a single-connected variable capacitor generally have 2 to 3 pins, that is, two internal pins and a ground pin.

3 Double variable capacitors

A double-connected variable capacitor can be simply understood as a combination of two single-connected variable capacitors.

The internal structure of the double-connected variable capacitor is similar to that of the single-connected variable capacitor. A rotating shaft drives the moving pieces of the two single-connected variable capacitors to rotate synchronously. When adjusting the shaft, the capacitance of the two single-connected variable capacitors changes synchronously.

Each of the two single-connected variable capacitors comes with a compensation capacitor for fine-tuning, so two adjustment holes can generally be seen from the back.

Generally, single-connected variable capacitors, double-connected variable capacitors, and quad-connected variable capacitors can be identified by the number of pins and back compensation capacitors.

The number of pins of a double-connected variable capacitor is generally 5, that is, 4 internal pins plus a ground pin.

There are two compensation capacitors inside the double-connected variable capacitor, and the adjustment holes of the two compensation capacitors can be seen from the back.

4 Quadruple Variable Capacitors

The quadruple variable capacitor contains 4 single variable capacitors that can be adjusted synchronously.

If it is a double-connected variable capacitor, two compensation capacitors can be seen from the back; if it is a quad-connected variable capacitor, four compensation capacitors can be seen from the back.

In addition, it is worth noting that due to different production processes, the number of pins of variable capacitors is not completely uniform. Usually, the number of pins of a single-connected variable capacitor is generally 2 to 3 (two internal pins plus a ground pin); the number of pins of a double-connected variable capacitor does not exceed 7; the number of pins of a quad-connected variable capacitor The number of pins is 7 to 9.

The number of pins of a quadruple variable capacitor is generally 7 to 9.

Each of the four single-connected variable capacitors comes with a compensation capacitor for fine-tuning, which can generally be seen from the back.

Variable capacitors can also be divided into film dielectric variable capacitors and air dielectric variable capacitors according to different media.

The film dielectric variable capacitor uses mica or plastic (polystyrene, etc.) film as the medium, and its shell is transparent plastic, which has the characteristics of small size, light weight, small capacitance and easy to wear. Air is used as the medium between the moving plate and the stator of the air-dielectric variable capacitor, which is mostly used in radios, high-frequency signal generators, communication equipment and related electronic equipment. Common air dielectric variable capacitors mainly include air single-connected variable capacitors (air single-connected) and air double-connected variable capacitors (air double-connected).

The film dielectric variable capacitor uses mica or plastic (polystyrene, etc.) film as the medium between the moving piece and the fixed piece (the moving piece and the fixed piece are irregular semi-circular metal pieces).

The electrodes of the air dielectric variable capacitor are composed of two groups of metal sheets. Among them, the fixed group is the fixed piece, the rotatable group is the moving piece, and the air is used as the medium between the moving piece and the fixed piece.