Many electronic products, electronic components capacitors are essential, it acts as a smoothing rectifier in electronic devices, power and decoupling, bypass the AC signal, AC-coupled AC and DC circuit and the like. Because of the type of capacitor type and structure are more, so users only need to understand the performance of various types of capacitors and general characteristics, but also must understand the advantages and disadvantages of a given, mechanical or environmental conditions limit the use of various elements of the next and so on . The main parameters are presented below and the application of the capacitor, when used for readers to choose the type of capacitor.
1, the nominal capacity (CR): Products marked capacitor capacitance value.
Lower capacity electric capacitors mica and ceramic media (approximately 5000pF or less); paper, plastic, and some form of electrical capacitance ceramic media center (about 0005μF10μF); usually larger capacity electrolytic capacitor. This is a rough taxonomy.
2, category temperature range: capacitor design can be determined by continuous ambient temperature range, which depends on its temperature limit corresponding category, such as the upper category temperature, the lower category temperature and the rated temperature (maximum rated voltage may be applied continuously for ambient temperature) and the like.
3, rated voltage (UR): at any temperature lower category temperature and the rated temperature between, can be continuously applied to the capacitor rms or peak pulse voltage maximum DC voltage or maximum AC voltage.
When the capacitor is used in high-pressure situations, we must pay attention to the impact of corona. Corona is due to the gap between the dielectric / electrode layer is generated, it can generate spurious signals in addition to damage to the equipment, it will also lead to the capacitor dielectric breakdown. Under conditions of AC or pulsating corona particularly prone. For all of the capacitors in use should ensure that the DC voltage and peak voltage of the AC and DC voltage rating not exceeding.
4, loss tangent (tanδ): sinusoidal voltage at a predetermined frequency, the capacitor power loss divided by the capacitor reactive power.
It should explain, in practical applications, the capacitor is not a pure capacitance, as well as its internal equivalent resistance, its simplified equivalent circuit is shown below. Figure C is the actual capacitance of the capacitor, Rs is the equivalent series resistance of the capacitor, Rp is a dielectric insulation resistance, Ro is the equivalent resistance of the absorption medium. For electronic equipment, requires Rs smaller the better, that requires little power loss, with the capacitance of the power angle δ small.
This relationship is expressed by the following formula: tanδ = Rs / Xc = 2πf × c × Rs Therefore, the application of which should be selected in this parameter, to avoid self-heating is too large, in order to reduce the failure of the equipment.
5, the temperature characteristics of the capacitor: usually 20 ℃ temperature reference capacitance and temperature related capacitance percentage representation.