Fixed capacitors are capacitors with fixed capacitance, which can be divided into two categories: ceramic capacitors and mica capacitors.
♦ ceramic capacitor
- Ceramic capacitors are made by extruding a high-dielectric constant capacitor ceramic (barium titanate titanium monoxide) into a tube, a wafer or a disc as the medium, and plating silver on the ceramic as an electrode by the firing method. It is divided into high-frequency porcelain and low-frequency porcelain.
- High-frequency ceramic capacitors are suitable for high-frequency circuits in radio and electronic equipment. Capacitors with small positive capacitance temperature coefficients are used in highly stable oscillation circuits as loop capacitors and pad capacitors. Low-frequency ceramic capacitors are limited to be used in circuits with lower operating frequencies to bypass or block DC, or to use in situations where stability and loss are not high (including high frequencies). They are not suitable for use in pulse circuits. Because they are easily broken down by pulse voltage. Common ceramic dielectric capacitors have through-core or pillar structure ceramic dielectric capacitors, one of its electrodes is a mounting screw.
- Monolithic capacitors are multilayer ceramic capacitors. Its structure is to cover several pieces of ceramic film blanks with electrode paddle materials, which are wound into an indivisible whole after being laminated, and then encapsulated with resin. It is a small A new type of capacitor with volume, large capacity, high reliability and high temperature resistance; low-frequency monolithic capacitors with high dielectric constant also have stable performance and small size.
♦ Mica capacitor
- In terms of structure, mica capacitors can be divided into foil type and silver type. The silver type electrode is directly coated with a silver layer on the mica sheet by vacuum evaporation or burning infiltration. Because the air gap is eliminated, the temperature coefficient is greatly reduced, and the capacitance stability is higher than that of the foil type. Mica capacitors are widely used in high-frequency electrical appliances and can be used as standard capacitors.