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Some customers will ask about the use and purchase of aluminum Electrolytic capacitor,Dongguan Youchen Electronic Technology Co., LtdHere is a summary of relevant techniques for your reference:
The aluminum Electrolytic capacitor is made of an aluminum cylinder as the negative electrode, which is filled with liquid electrolyte and inserted with a curved aluminum strip as the positive electrode. It also requires direct current voltage treatment to form a layer of oxide film on the positive electrode as the medium. Its characteristics are large capacity, but high leakage, poor stability, and positive and negative polarity, making it suitable for power filtering or low-frequency circuits.
Capacity and rated working voltage
The capacity and withstand voltage marked on the aluminum Electrolytic capacitor body are very important and are the most basic content for selecting capacitors.
In actual capacitor selection, larger capacitors should be used for areas with fast current changes, but it is not necessarily better to have larger capacities. Firstly, as the capacity increases, the cost and volume may increase. Additionally, the larger the capacitor, the greater the charging current and the longer the charging time. These are all considerations to consider in practical application selection.
Rated working voltage: The maximum DC voltage that a capacitor can withstand when operating reliably for a long time within the specified working temperature range. In AC circuits, it is important to note that the maximum AC voltage applied cannot exceed the DC operating voltage of the capacitor. The commonly used fixed capacitor working voltages include 6.3V, 10V, 16V, 25V, 50V, 63V, 100V, 250V, 400V, 500V, and 630V. The actual voltage that a capacitor must withstand in a circuit cannot exceed its withstand voltage value.
In the filtering circuit, the withstand voltage value of the capacitor should not be less than 1.42 times the AC effective value. Another issue that needs to be noted is the issue of working voltage capacity, which generally needs to be above 15%.
Allowing the rated voltage of capacitors to have more margin can reduce internal resistance, reduce leakage current, reduce loss angle, and increase service life. Although the use of 50V aluminum Electrolytic capacitor with 48V working voltage will not cause problems in a short time, the service life may be reduced after long use.
The energy consumed by a capacitor under the action of an electric field is usually represented by the ratio of the loss power to the reactive power of the capacitor, which is the tangent of the loss angle (in the equivalent circuit of a capacitor, the series equivalent resistance ESR is the same as the capacitance reactance 1/ ω The ratio of C is called Tan δ， The ESR here is the value calculated at 120Hz. Obviously, Tan δ It increases with the increase of measurement frequency and increases with the decrease of measurement temperature. The larger the loss angle, the greater the loss of the capacitor. A capacitor with a larger loss angle is not suitable for working at high frequencies. The dissipation factor (DF) exists in all capacitors, and sometimes the DF value will vary with the loss angle tan δ Represent. The lower this parameter, the better. But this parameter of Aluminium electrolytic capacitor is relatively high.
Whether the DF value is high or low is related to temperature, capacity, voltage, frequency, etc. for capacitors of the same brand and series; When the capacity is the same, the higher the withstand voltage, the lower the DF value. In addition, the higher the temperature, the higher the DF value, and the higher the frequency, the higher the DF value.
The external dimensions are related to weight and joint shape. Singleended is of radial lead type, screw is of locking screw type, and there is also an aluminum Electrolytic capacitor chip. Compared to two capacitors with the same capacity and voltage resistance, but different brands, the weight must be different; And the overall size is more related to the shell planning. Generally speaking, capacitors with the same diameter and capacity can be replaced by capacitors with lower heights. However, when replacing capacitors with lower lengths, the issue of mechanism interference should be considered.
ESR Equivalent series resistance and ESL Equivalent series inductance are a pair of important parameters - this is the basis of capacitive reactance. A capacitor with a small Equivalent series resistance (ESR) can well absorb the peak (ripple) current during fast conversion compared with an external capacitor with a large capacity. Shunting capacitors with larger ESR is more cost-effective. However, this requires seeking a compromise between PCB area, number of devices, and cost.
Ripple current and ripple voltage
Also known as ripple current and ripple voltage, they are actually ripple current and ripple voltage. The meaning is the ripple current/voltage value that a capacitor can withstand. The ripple voltage is equal to the product of the ripple current and ESR.
When the ripple current increases, even while the ESR remains constant, the ripple voltage will increase exponentially. In other words, as the ripple voltage increases, the ripple current also increases, which is why capacitors are required to have lower ESR values. After adding ripple current, the equivalent series resistance (ESR) inside the capacitor causes heat generation, which affects the service life of the capacitor. Generally, the ripple current is proportional to the frequency, so the ripple current is also relatively low at low frequencies.
The rated ripple current is a numerical value defined under the highest operating temperature conditions. In practical applications, the ripple tolerance of capacitors is also related to their operating environment temperature and the temperature level of the capacitor itself. The specification book usually provides the maximum ripple current that capacitors of each temperature level can withstand under specific temperature conditions. Even provide a detailed chart to help users quickly find the allowable capacitance ripple amount to achieve a certain expected service life under certain environmental temperature conditions.
The medium of a capacitor has a significant hindrance to DC current. However, due to the presence of electrolyte on the aluminum oxide film medium, a small current called leakage current is generated during voltage application, reconstruction, and repair of the oxide film. Usually, the leakage current increases with the increase of temperature and voltage. Its calculation formula is roughly: I=K × CV. The unit of leakage current I is μ A. K is a constant. Generally speaking, the higher the capacity of a capacitor, the greater the leakage current. From the formula, it can be inferred that the higher the rated voltage, the greater the leakage current. Therefore, reducing the working voltage can also reduce the leakage current.
First of all, make it clear that the aluminum Electrolytic capacitor will be broken. It is only a matter of time. There are many reasons that affect the lifespan of capacitors, such as overvoltage, reverse voltage, high temperature, rapid charging and discharging, etc. Under normal use, the biggest impact is temperature, because the higher the temperature, the faster the evaporation loss of the electrolyte. It should be noted that the temperature here does not refer to the environment or surface temperature, but rather to the working temperature of the aluminum foil. Manufacturers usually label the capacitor life and testing temperature on the capacitor body.
Since the service life of the capacitor is halved every time the working temperature of the capacitor increases by 10 ℃, do not think that the aluminum Electrolytic capacitor with a service life of 2000 hours is better than that of 1000 hours. Pay attention to the test temperature to confirm the service life. Each manufacturer has calculation formulas for temperature and life, and the design of capacitance shall refer to actual data for calculation. What we need to know is that to improve the life of aluminum Electrolytic capacitor, first, we should reduce the operating temperature and keep away from heat sources on the PCB. Second, we should consider using capacitors with high maximum operating temperature. Of course, the price will also be higher.
The resistance that hinders the passage of AC current at a specific frequency is called impedance. It is closely related to the capacitance and inductance values in the capacitance equivalent circuit, and is also related to ESR. The capacitance impedance of the capacitor gradually decreases with the increase of frequency within the low-frequency range, and the reactance decreases to the value of ESR when the frequency continues to increase and reaches the intermediate frequency range. When the frequency reaches the high-frequency range, the inductance becomes dominant, so the impedance increases with the increase of frequency.
The output filtering Electrolytic capacitor in the switching power supply has a Sawtooth wave voltage frequency up to tens of kHz, even tens of MHz. At this time, the capacitance is not its main indicator. The standard to measure the quality of high-frequency aluminum Electrolytic capacitor is the "impedance frequency" characteristic. It requires a low equivalent impedance within the operating frequency of the switching power supply, and has a good filtering effect on the high-frequency spike signals generated when semiconductor devices work