Teach you how to use a multimeter to determine the positive and negative poles of electrolytic capacitors
In the design of electronic circuits, electrolytic capacitors pass AC and DC, and are also used to store and release charges to act as filters to smooth output pulsating signals. How to distinguish the positive and negative electrodes of electrolytic capacitors in circuit design? If it is reversed, it is dangerous. Large-capacity capacitors may even explode. Let’s take a look at how to use a multimeter to determine the positive and negative electrodes of electrolytic capacitors.
1. Introduction to electrolytic capacitors
Electrolytic capacitor is a kind of capacitor, the metal foil is the positive electrode (aluminum or tantalum), the oxide film (aluminum oxide or tantalum pentoxide) close to the positive electrode is the dielectric, and the cathode is made of conductive material and electrolyte (the electrolyte can be liquid or tantalum pentoxide). Solid) and other materials together, because the electrolyte is the main part of the cathode, so the electrolytic capacitor is named. At the same time, the positive and negative electrolytic capacitors should not be wrongly connected.
Electrolytic capacitors are divided into two types: non-polar and polar. Non-polar electrolytic capacitors use a double oxide film structure, similar to two polar electrolytic capacitors that connect two negative electrodes; polar electrolytic capacitors are usually used in power circuits or In the intermediate frequency and low frequency circuits, it plays the role of power supply filtering, decoupling, signal coupling, time constant setting, and DC blocking.
2. The role of electrolytic capacitors
Electrolytic capacitors are widely used in household appliances and various electronic products. Polarized electrolytic capacitors usually play the role of power supply filtering, decoupling, signal coupling, time constant setting, and DC blocking in power supply circuits or intermediate frequency and low frequency circuits. Non-polar electrolytic capacitors are usually used in speaker divider circuits, TV S correction circuits and single-phase motor starting circuits. The functions of electrolytic capacitors are mainly divided into the following categories:
1) Blocking DC - the function is to prevent DC from passing through and allow AC to pass.
2) Filtering----In the power supply circuit, the rectifier circuit turns the AC into a pulsating DC, and after the rectifier circuit, a large-capacity electrolytic capacitor is connected, and its charge and discharge characteristics (energy storage effect) are used to make the rectifier. The pulsating DC voltage then becomes a relatively stable DC voltage.
3) Coupling ---- In the process of low-frequency signal transmission and amplification, capacitive coupling is often used to prevent the static operating points of the front and rear circuits from affecting each other. As a connection between two circuits, it allows the AC signal to pass through and be transmitted to the next stage circuit.
4) Bypass—Provides a low-impedance path for some parallel components in an AC circuit.
5) Energy storage ---- store electrical energy for release when necessary.
6) Temperature compensation----Compensate for the influence of insufficient adaptability of other components to temperature to improve the stability of the circuit.
7) Tuning - System tuning of frequency-related circuits, such as mobile phones, radios, and televisions.
3. Use a multimeter to determine the positive and negative poles of the electrolytic capacitor
Electrolytic capacitors are divided into positive and negative poles. Generally, the long lead is the positive pole, and the short lead is the negative pole, and is marked with "one".
When testing the quality of the electrolytic capacitor, turn the multimeter to RXlk, the red test lead is connected to the negative electrode of the electrolytic capacitor, and the black test lead is connected to its positive electrode. It deflects to the left again, that is, it falls back in the direction of infinity and stabilizes. At this time, the value indicated by the needle is the forward leakage resistance of the capacitor. The larger the forward leakage resistance of an electrolytic capacitor, the smaller the corresponding leakage current. Generally, the forward leakage resistance of a capacitor is about tens of kiloohms or more than several hundred kiloohms, as shown in Figure 2-19. If the capacitance of the capacitor is greater than 10uF, in order to prevent the needle from being bent, the leads at both ends of the capacitor should be short-circuited before measurement to release the charged charge of the capacitor.
The quality of an electrolytic capacitor depends not only on the magnitude of its forward leakage resistance, but also on the swing amplitude of the needle during detection. The more the pointer swings to the right, the greater the capacity of the electrolytic capacitor. If the leakage resistance value is several hundred thousand ohms, but the pointer does not swing at all, it means that the electrolyte of the capacitor has dried up and failed and cannot be used. If the needle does not return to "0" during the test, it means that the capacitor has been broken down or short-circuited.
