Electrolytic capacitors play a key role in electronic circuits and their functions are widespread and important. The following will discuss the key role of electrolytic capacitors in circuit design and the key points that need to be paid attention to when using them.
Filtering: In the power circuit, the rectifier circuit converts alternating current into pulsating direct current, but this still contains some fluctuations. By connecting a larger-capacity electrolytic capacitor and utilizing its charging and discharging characteristics, the pulsating DC voltage can be turned into a relatively stable DC voltage. In order to maintain the stability of the supply voltage of each part of the circuit, electrolytic capacitors from tens to hundreds of microfarads are usually connected to the power output end and the load power input end. Since large-capacity electrolytic capacitors have a certain inductance and cannot effectively filter out high-frequency and pulse interference signals, a capacitor with a capacity of 0.001 to 0.1 microfarad is usually connected in parallel to filter out high-frequency and pulse interference signals.
Coupling effect: In the process of low-frequency signal transmission and amplification, in order to prevent the static operating points of the front and rear circuits from affecting each other, capacitors are often used to achieve coupling. In order to retain the low-frequency components in the signal, electrolytic capacitors with larger capacities are usually used.
The judgment methods and precautions for electrolytic capacitors are as follows:
To judge the quality of electrolytic capacitors: usually use the resistance range of a multimeter to measure. First, short-circuit both ends of the capacitor to discharge, then use the black test lead of the multimeter to touch the positive electrode of the electrolytic capacitor and the red test lead to the negative electrode. Under normal circumstances, the meter needle should swing in the direction of smaller resistance value, and then gradually return to infinity. If the needle swings widely or returns slowly, it indicates that the capacitor capacity is large. On the contrary, if the hands of the meter no longer change at a certain position, it indicates that the capacitor is leaking. If the resistance value is very small or zero, it indicates capacitor breakdown or short circuit.
Precautions for use:
Electrolytic capacitors have polarity and should not be connected upside down. In a power supply circuit, a positive voltage should connect the positive terminal of the electrolytic capacitor to the power supply output, and a negative voltage should connect the positive terminal to the power supply output and the negative terminal to ground. Connecting electrolytic capacitors with reverse polarity can cause circuit instability or even capacitor rupture.
The voltage should not exceed the rated operating voltage of the electrolytic capacitor. When designing the circuit, a certain voltage margin should be left to cope with voltage fluctuations in the power circuit. If the AC power supply voltage may exceed the rated operating voltage, an electrolytic capacitor with a higher rated operating voltage should be selected.
Avoid placing electrolytic capacitors close to high-power heating elements to avoid accelerated evaporation of the electrolyte.
For filtering of positive and negative polarity signals, two electrolytic capacitors of the same polarity can be connected in series to simulate a non-polar capacitor.
The capacitor housing, terminals, and positive and negative poles must be completely isolated to avoid short circuits or other malfunctions.
To sum up, electrolytic capacitors play an important role in circuit design, but their polarity, voltage, location and other factors need to be carefully considered when using them to ensure the normal operation and stability of the circuit.