Capacitance is a scalar device used to store the value of the capacitance unit in the electromagnetic system of units. Its characteristic is that the capacitance is very accurate and stable, commonly used as a measuring standard or installed in electrical measuring instruments as a standard capacitance component. Standard electrical appliances are usually in the decimal system, with a capacitance range of 1 picnF to 1 microfa. In special cases, they can also be made into smaller or larger values, or non decimal values.

Basic error of capacitors δ Determination of.

a. For capacitors with accuracy levels of 1,0.5, the total measurement error caused by standard instruments, testing methods, and testing conditions should not exceed two tenths of the allowable basic error limit. The test results should comply with the provisions of Article 3.1 of this standard.

b. For capacitors of other accuracy levels, the total measurement error caused by standard instruments, testing methods, and testing conditions should not exceed one-third of the allowable basic error limit, and the test results should comply with the provisions of Article 3.1 of this standard.

1、 Annual Instability of the Actual Capacity of Guoju Proxy Capacitors γ Determination of. The determination of the annual instability of the actual value of capacitor capacity is represented by the relative error calculated by comparing the current and previous measured values. The test results should comply with the provisions of Table 3 in Article 3.4 of this standard. The standard instruments used should not be replaced, and their annual instability and testing process accuracy should not exceed one tenth of the allowable basic error limit of the tested capacitor.

2、 Determination of the tangent value D of the loss angle of Guoju's proxy capacitor

3、 For loss angle tangent value D greater than 5 × The total measurement error caused by standard instruments, testing methods, and testing conditions for capacitors of 10-3 should not exceed one-third of the allowable loss angle tangent value D. The test results should comply with the provisions of Article 3.5 of this standard.

4、 For loss angle tangent value D less than or equal to 5 × 10-3 and greater than or equal to 1 × The total measurement error caused by standard instruments, testing methods, and testing conditions for capacitors of 10 to 4 should not exceed half of the allowable loss angle tangent value D, and the test results should comply with the provisions of Article 3.4 of this standard.

5、 For loss angle tangent value D less than 1 × The total measurement error caused by the testing instrument, testing method, and testing conditions for capacitors of 10 to 4 should not exceed the allowable loss angle tangent value D, and the test results should comply with the provisions of Article 3.5 of this standard.

To have a deeper understanding of capacitors:

1、 The larger the capacitance, the better

Many people often prefer to use large capacity capacitors in the replacement of capacitors. We know that although the larger the capacitance, the stronger the current compensation ability provided for the IC. Not to mention the increase in capacitor capacity, which leads to a larger volume and increases costs, it also affects air flow and heat dissipation. The key lies in the presence of parasitic inductance on the capacitor, and the capacitor discharge circuit will resonate at a certain frequency point. At the resonance point, the impedance of the capacitor is small. Therefore, the impedance of the discharge circuit is the smallest, and the effect of supplementing energy is also the best. But when the frequency exceeds the resonance point, the impedance of the discharge circuit begins to increase, and the capacitance's ability to provide current begins to decrease. The larger the capacitance value of the capacitor, the lower the resonant frequency, and the smaller the frequency range in which the capacitor can effectively compensate for the current. From the perspective of ensuring the ability of capacitors to provide high-frequency current, the viewpoint that larger capacitors are better is incorrect. Generally, there is a reference value in circuit design.

2、 A capacitor of the same capacity is not necessarily better with more small capacitors in parallel

Voltage withstand value, temperature resistance value, capacitance value, ESR (equivalent resistance), etc. are several important parameters of capacitors, and the lower the ESR, the better. ESR is related to the capacity, frequency, voltage, temperature, etc. of capacitors. When the voltage is fixed, the larger the capacity, the lower the ESR. The use of multiple small capacitors connected in parallel in board design is a limitation of PCB space. Some people believe that the more small resistors connected in parallel, the lower ESR, and the better the effect. In theory, this is the case, but considering the impedance of the capacitor pin solder joint, using multiple small capacitors in parallel may not necessarily result in outstanding results.

3、 The lower the ESR, the better the effect

Based on the improved power supply circuit provided by Guoju's agents, the capacity of the input capacitor should be slightly larger. The requirement for relative capacity can be appropriately reduced for ESR. Because the input capacitor is mainly used for withstand voltage, followed by absorbing MOSFET switching pulses. For output capacitors, the requirements and capacity for withstand voltage can be appropriately reduced. The requirements for ESR are a bit higher because what needs to be ensured here is sufficient current flow. But it should be noted that the lower the ESR, the better. Low ESR capacitors can cause switching circuit oscillations. The complexity of the vibration suppression circuit can also lead to an increase in cost. In board design, there is usually a reference value here, which serves as a parameter for component selection to avoid cost increases caused by vibration reduction circuits.

4、 Good capacitors do not necessarily mean high quality

The theory of only capacitance was once in its heyday, and some manufacturers and media deliberately made this a selling point. In board design, the level of circuit design is crucial. Just like some manufacturers who can use two-phase power supply to produce more stable products than some manufacturers who use four-phase power supply, blindly using expensive capacitors may not necessarily result in good products. When measuring a product, it is necessary to consider it from all angles and perspectives, and the role of capacitors should not be intentionally or unintentionally exaggerated.