How to distinguish the polarity of capacitors

How to distinguish the polarity of capacitors

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Capacitors are one of the most common electronic components, and more importantly, they can be polarized or non-polarized. Polarized capacitors are typically electrolytic or tantalum capacitors. The polarity of these capacitors is marked on the circuit board, making it easy to distinguish the positive and negative terminals based on their packaging and dimensions once you have the board.

Here is a brief introduction to common methods for identifying capacitor polarity, which you must understand if you are about to use capacitors.

  1. Distinguishing the polarity of through-hole electrolytic capacitors
    The polarity of through-hole electrolytic capacitors can be identified by the length of the leads and the color of the casing. The longer lead is the positive terminal, while the shorter lead is negative. The grey-colored area on the casing corresponds to the negative lead, with the opposite end being positive.
    If the capacitor is packaged, the positive terminal is usually marked with a “+” symbol, or the negative terminal is indicated by a colored area.

  2. Distinguishing the polarity of surface-mount aluminum electrolytic capacitors
    Surface-mount aluminum electrolytic capacitors are often used in large-scale SMT mounting to improve soldering efficiency, though they generally have smaller capacitance than through-hole types. Viewed from the base, the rounded corner corresponds to the positive terminal, and the straight edge to the negative terminal.
    On the circuit board, the colored area typically indicates the negative terminal, with the other end being positive.

  3. Distinguishing the polarity of tantalum capacitors
    The polarity of surface-mount tantalum capacitors can be identified by the stripe on the casing. The end with the stripe is the positive terminal, while the other end is negative.
    On a PCB, the smaller area corresponds to the positive terminal, or the side with the stripe or “+” symbol is positive.
    Note that the markings on tantalum capacitors resemble those of surface-mount diodes but are reversed.

  4. Distinguishing the polarity of bolt-type electrolytic capacitors
    It is critical to distinguish the positive and negative terminals when using bolt-type electrolytic capacitors, as reversing them can be very dangerous. First, check the marking on the white or silver edge; a dash symbol indicates the negative terminal, while a “+” symbol indicates the positive terminal.
    If the capacitor is new, you can also judge polarity by the lead length, with the longer lead being positive, and then check the symbol on the silver edge to confirm.

  5. CBB and AC capacitors
    CBB capacitors, commonly found in household appliances, are non-polarized. When using them, be sure to pay attention to the voltage rating.

  6. Ceramic, porcelain, and surface-mount capacitors
    Ceramic, porcelain, and surface-mount capacitors are non-polarized, meaning they do not have distinct positive and negative terminals. These capacitors typically have small capacitance and are often used for signal filtering. Any observed polarity is temporary. As a type of non-polarized electrolytic capacitor, they do not require polarity recognition during installation and can be mounted in any orientation.

Identifying Capacitor Polarity with a Multimeter

Although capacitor polarity is often easily determined by its appearance, some may not be familiar with its identifying characteristics. Using a multimeter to check capacitor polarity is a common method. By using specialized equipment, we can ensure accurate results.

The basic principle is that when the anode of an electrolytic capacitor is connected to the positive terminal of a power source (with the black lead of the multimeter for resistance measurement) and the cathode to the negative terminal (with the red lead), the current passing through the capacitor will be small (i.e., the leakage resistance will be high). Otherwise, the leakage current of the capacitor will be large.

 

Testing Method with a Multimeter:

  1. To measure, first assume one lead is the anode and connect it to the black lead of the multimeter, then connect the other lead to the red lead.
  2. Observe the reading when the needle stops (the value on the left side of the dial is higher). It is best to set the multimeter to R100 or R1K for measurement.
  3. Discharge the capacitor (to remove any stored charge), then switch the multimeter leads and measure again.
  4. In the two tests, the one in which the needle stops on the left (with a higher resistance value) indicates that the black lead is connected to the capacitor’s anode.

Precautions:

  • Before measuring, use a resistor or additional wire to discharge any residual charge from the capacitor.
  • Since the measurement involves a charging process, the reading may take some time to stabilize.
  • In analog multimeters, the black lead is positive, and the red lead is negative, while in digital multimeters, the polarity is reversed.

Capacitor Functions

  • Coupling: A capacitor used in coupling circuits is called a coupling capacitor. It is widely used in RC-coupled amplifiers and other capacitor-coupled circuits to block DC while allowing AC to pass.
  • Filtering: Capacitors used in filtering circuits are called filter capacitors. These capacitors are used in power supply filtering and various filter circuits to remove certain frequency signals from the overall signal.
  • Decoupling: A capacitor used in decoupling circuits is called a decoupling capacitor. It is used in the DC voltage supply circuits of multi-stage amplifiers to eliminate harmful low-frequency inter-stage coupling.
  • High-Frequency Stabilization: Capacitors used in high-frequency stabilization circuits are called high-frequency stabilization capacitors. In audio negative feedback amplifiers, this type of capacitor circuit is used to eliminate potential high-frequency oscillations and prevent high-frequency feedback whistling.

Conclusion

By considering appearance, structure, materials, application, and performance, we can effectively identify capacitor polarity. In practical use, always carefully check the markings and documentation to ensure correct connection and operation.