The selection of capacitor components in PCBA processing should consider the following factors:
1、 Capacitor withstand voltage selection
When selecting capacitors, the withstand voltage of the components must be higher than the actual working voltage in the circuit, especially when considering the potential high voltage generated in electronic circuits.
2、 Selection of capacitance and capacitance
In electronic circuits, capacitance is determined based on certain performance indicators, and when determining capacity, it should be selected based on the nominal series. If the capacity value of the capacitor cannot be found through the nominal series, it can be solved through series parallel connection or by modifying other parameters in the design scheme. When replacing capacitors in a circuit, it is best to choose capacitors with original parameters or components with better performance indicators than the original circuit capacitors.
3、 Selection of capacitor medium
Different dielectric capacitors have significant differences in their characteristics and different uses. When choosing a dielectric for capacitors, it is important to first understand the characteristics of each medium and then determine the appropriate occasion.
Below are several commonly used fixed capacitors:
1. The Electrolytic capacitor takes aluminum and other metals as the positive pole, forms a layer of oxide film on its surface as the medium, and the medium and electrode become an inseparable whole; The negative electrode is a solid or non solid electrolyte. Since the materials of the two electrodes constituting the Electrolytic capacitor are different, their positive and negative electrodes are marked respectively. When using, the positive terminal must be connected to the high potential of the circuit, and the negative terminal must be connected to the low potential of the circuit, otherwise the capacitor will be damaged. According to different electrode materials, there are aluminum Electrolytic capacitor, tantalum Electrolytic capacitor and niobium Electrolytic capacitor.
2. Mica capacitors are capacitors with mica sheets as the medium. It has good insulation performance, low loss, good temperature stability, and high capacitance accuracy, and is commonly used in high-frequency oscillation circuits.
3. The medium of ceramic dielectric capacitors is ceramics, which can be divided into two types based on different ceramic components: high-frequency ceramic dielectric capacitors and low-frequency ceramic dielectric capacitors (high-frequency ones are represented by CC and low-frequency ones by CT). The capacitance of high-frequency ceramic dielectric capacitors ranges from a few tenths of picoseconds to several hundred picoseconds. It is often used in situations where low loss and stable capacitance are required, and as a tuning capacitor, oscillation circuit capacitor, and temperature compensation capacitor in high-frequency circuits. There are several types of capacitor withstand voltage, including 160V, 250V, and 500V. The capacity error is divided into several types: 2%, 5%, 10%, and 20%. The low-frequency ceramic dielectric capacitance ranges from 300pF to 22000pF, suitable for low-frequency circuits.
4. The production process of paper capacitors is simple, cost-effective, and has a wide voltage range; The disadvantage is that the capacitance is difficult to control, the loss is large, the stability is poor, and the inductance is the largest, which is usually not suitable for use at high frequencies.
5. Polyester capacitors, also known as polyester capacitors. It is a capacitor made of polyester film as the dielectric. It can be used in various electronic instruments and meters, as well as in circuits such as coupling, decoupling, bypass, and DC isolation of televisions and recorders.
