The advantages of chip capacitors: small size, high temperature resistance, ripple suppression, high reliability, and long life
Capacitors are the basic components in circuits. Aluminum electrolytic capacitors are widely used because of their low price and large capacity. With the miniaturization of electronic products, electrolytic capacitors are gradually replaced by chip capacitors due to their large size and self-heating caused by ripple currents.
With the development of technology, the volume of MLCC can be made smaller and smaller, reaching 0201, and the capacitance value is continuously increasing, which has the advantages of saving space, suppressing ripple, and prolonging life, making it a the advantages of chip capacitors. However, the small ESR (Equivalent Series Resistance) of MLCC has an inverse effect. Due to abnormal vibration and anti-resonance, special attention must be paid to replacement.
- With the advancement of technology, large-capacity MLCCs of more than 10 to 100 μF have been commercialized, so that they can be used to replace electrolytic capacitors. The life of electrolytic capacitors is 10 years, but there are almost no elements that will shorten the life of MLCC.
- The electrolytic capacitor in the output capacitor is also continuously replaced by MLCC
- The use of analog circuits and other replacement decoupling capacitors is increasing.
Electrolytic capacitor with large capacity, but it will easily cause short life due to its own heat
The ESR of a capacitor will change depending on the frequency.
Representing the ESR of a capacitor at a certain frequency as R and the ripple current as I, the power of RI2 will be thermally lost, thus causing the capacitor to heat itself.
Electrolytic capacitors have the characteristics of large capacity, but because their ESR is too high, the excessive current generated by the ripple current is the disadvantage.
The upper limit of the ripple current acceptable to the capacitor is called the allowable ripple current. If the allowable ripple current is exceeded during use, the life of the capacitor will be shortened.
The ideal capacitor is an element with only electrostatic capacity, but in reality, it also has a resistance component and an inductance component due to the electrodes. The resistance component that cannot be identified in the circuit diagram is called ESR (equivalent series resistance), and the inductance component is called ESL (equivalent series inductance).
Although the DC current is a current flowing in one direction at a certain voltage, the DC current of the power circuit is superimposed with various AC components such as noise current. For example, the DC current obtained by rectifying commercial AC power (full-wave rectification) includes a microwave (ripple) -like pulsating current with a period twice that of commercial AC power. At the same time, in the switching DC-DC converter, the direct current voltage overlaps with the pulsating current of the switching cycle. These are called ripple currents.