Views: 6 Author: Site Editor Publish Time: 2021-10-13 Origin: Site
1. Select capacitors according to the specific requirements of the application circuit
There are many types of capacitors, and which type of capacitor should be selected according to the specific requirements of the application circuit.
Generally, the capacitors used in high-frequency and ultra-high-frequency circuits should select mica capacitors, glass glaze capacitors or high-frequency (Class I) ceramic capacitors. Paper capacitors, metallized paper capacitors, organic film capacitors, low-frequency (Class II, III) ceramic capacitors, electrolytic capacitors, etc., are generally used in medium and low-frequency circuits. In the tuning circuit, solid dielectric sealed variable capacitors, air dielectric capacitors and trimmer capacitors can be selected.
The main parameters (including nominal capacity, allowable deviation, rated working voltage, insulation resistance, etc.) and dimensions of the selected capacitor should also meet the requirements of the application circuit.
2. Selection of electrolytic capacitors
Electrolytic capacitors are mainly used in power circuits or medium and low frequency circuits for power supply filtering (100~1000μF), decoupling (47~220μF), low frequency circuit inter-stage coupling (1~22μF), low frequency bypass, time constant setting and dc isolation capacitors.
In general power circuits and medium and low frequency circuits, aluminum electrolytic capacitors can be used. Frequency division capacitors for speakers, TV S correction capacitors and motor starting capacitors can be selected as non-polar aluminum electrolytic capacitors. In the circuits of communication equipment and various high-precision electronic equipment, non-solid tantalum electrolytic capacitors or niobium electrolytic capacitors can be used.
When selecting an electrolytic capacitor, pay attention to its outer surface should be smooth, without dents or incompleteness, the plastic envelope should be intact, the marking should be clear, the pins should not be loose, and there should be no electrolyte leakage at the main parts of the pins.
3. Selection of solid organic dielectric capacitors
Among the solid organic dielectric capacitors, organic film dielectric capacitors are most used, such as polyester capacitors (CL series), polystyrene capacitors (CB series) and polypropylene capacitors (CBB series).
Dacron capacitors can be used as decoupling, bypass, and dc blocking capacitors in the medium and low frequency circuits of electronic equipment such as radios and televisions.
Polystyrene capacitors can be used in audio circuits and high-voltage pulse circuits, but cannot be used in high-frequency circuits.
Polypropylene capacitors have better high-frequency characteristics than polyester capacitors and polystyrene capacitors. In addition to being used in dc circuits and high-frequency pulse circuits of televisions, audio and other electronic equipment, they can also be used as starting and running capacitors for ac motors.
4. Selection of solid inorganic dielectric capacitors
Among the solid inorganic upgraded capacitors, ceramic capacitors are the most used, especially ceramic chip capacitors, monolithic capacitors and leadless ceramic capacitors.
High-frequency circuits and ultra-high frequency circuits should use Class I ceramic capacitors, and medium and low-frequency circuits can use Class II ceramic capacitors. Class III ceramic capacitors can only be used in low-frequency circuits, and cannot be used in medium and high-frequency circuits.
Coupling capacitors in high-frequency circuits, bypass capacitors, and fixed capacitors in tuning circuits can all be glass glaze capacitors or mica capacitors.
5. Selection of variable capacitor
Variable capacitors are mainly used for tuning circuits. Air dielectric variable capacitors were used in electronic tube radios and communication equipment in the early days, but now they are rarely used in electronic equipment; while solid dielectric variable capacitors are still widely used.
Generally, sealed double variable capacitors can be used for AM radios, and sealed four-connected variable capacitors can be used for AM/FM radios and radio(sealed four variable capacitors usually also have film semi-variable capacitors on the housing).