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Problems of Long life Electrolytic capacitor


The lifespan of chip capacitors has always been a question that many people are puzzled about. Many people do not know how long the lifespan of chip capacitors is and how long they have been used. So, let's introduce how to infer the lifespan of capacitors. Firstly, the lifespan of capacitors can be calculated through the voltage acceleration and temperature acceleration coefficients. The steps are as follows:

The external environmental temperature and applied voltage during product use can be formulated as parameters. Generally speaking, the Arrhenius rule is widely used in acceleration formulas, and we can use the following formula to make simple calculations.

47_ Based on this formula, the service life of the product can be calculated by conducting accelerated tests under more stringent conditions (higher temperatures, voltages). Here, let's compare the accelerated test of monolith Ceramic capacitor with the assumed environment of actual product use. We consider the endurance test time as LA in the acceleration test of capacitors, and the equivalent number of years in the actual usage environment as LN for the above formula.

Durability test conditions assume the use of environmental voltage acceleration coefficient, temperature acceleration coefficient, corresponding years TA=85 ° C VA=20V LA=1000h TN=65 ° C VN=5V n=4 θ= 8 LN=? In this way, we can conduct a durability test for 1000 hours at 85 ° C and applied a voltage of 20V, and calculate that the product's service life is 1448155 hours (≈ 165 years!) at 5 ° C and applied a voltage of 5V. The voltage acceleration coefficient and temperature acceleration coefficient used in the calculation may vary depending on the type and structure of ceramic materials, but the acceleration calculation formula can be used to verify the product's service life in a relatively short period of time using test results in a long-term actual usage environment.

      Long life Electrolytic capacitorThe identification and application of components are as follows:

First: Detection of capacitors

The main faults of capacitors are breakdown, short circuit, leakage, reduced capacity, deterioration, and damage.

1、 Visual inspection

The appearance should be intact and undamaged, with no cracks, dirt, or corrosion on the surface. The markings should be clear, and the lead out electrode should not be damaged; Adjustable capacitors should rotate flexibly, without any collision or friction between moving and fixed pieces, and the rotation between each connection should be synchronized.

2、 Testing leakage resistance

Use a multimeter in the Ohm range (R × 100 or R × 1k gear), contact the probe with the two leads of the capacitor. When it is just connected, the pointer of the meter will swing, and then gradually return to the point of R =∞, which is the charging and discharging phenomenon of the capacitor (for 0.1 μ This phenomenon cannot be observed for capacitors below F. The larger the swing of the pointer, the greater the capacity, and the value indicated by the stable pointer is the leakage resistance value. Its value is generally several hundred to several thousand megaohms, and the higher the resistance value, the better the insulation performance of the capacitor. When detecting, if the pointer on the meter head points to or near the zero point of the ohm, it indicates a short circuit inside the capacitor. If the pointer remains stationary and always points to R=∞, it indicates an open circuit or failure inside the capacitor.

Capacitors above 5000pF can be distinguished using a multimeter resistance range, while small capacity capacitors below 5000pF should be distinguished using specialized measuring instruments.

3、 Polarity detection of Electrolytic capacitor

The positive and negative polarity of Electrolytic capacitor is not allowed to be connected wrongly. When the polarity mark cannot be identified, it can be detected and judged according to the characteristics of large leakage resistance in forward connection and small leakage resistance in reverse connection. Measure the leakage resistance value twice before and after exchanging the probes, and when the larger resistance value is measured once, the black probe contacts the positive electrode. (Because the black probe is connected to the positive pole of the battery inside the meter)

4、 Detection of touch or leakage of variable capacitors

Dial the multimeter to R × At the 10th gear, two probes are placed on the movable and fixed pieces of the variable capacitor, and the movable pieces are slowly rotated. If the pointer of the meter head remains stationary, there is no contact or leakage; If it rotates to a certain angle and the pointer of the meter points to 0 Ω, it indicates that there is a contact plate here. If the pointer of the meter has a certain indication or slight swing, it indicates that there is leakage.

Second: Method of selecting capacitors

1、 Choose the appropriate model

According to the circuit requirements, it is generally used for low-frequency coupling, bypass decoupling, etc. When the electrical performance requirements are low, paper capacitors, Electrolytic capacitor, etc. can be used.

Coupling capacitors for transistor low-frequency amplifiers, selected from 1-22 μ F's Electrolytic capacitor. The bypass capacitor is selected according to the working frequency of the circuit. For example, in the low-frequency circuit, the emitter bypass capacitor is a Electrolytic capacitor with a capacity of 10-220 μ Between F; In intermediate frequency circuits, 0.01~0.1 can be selected μ F paper media, metallized paper media, organic thin film capacitors, etc; High frequency ceramic dielectric capacitors should be selected in high-frequency circuits; If it is required to work at high temperatures, glass glazed capacitors should be selected. In the power filter and decoupling circuit, Electrolytic capacitor can be selected. Because in these usage scenarios, the performance requirements for capacitors are not high, as long as the volume is small and the capacity is sufficient.

For variable capacitors, it should be determined based on the number of stages of capacitor tuning that single or multiple variable capacitors should be used. Then, the corresponding type of capacitor should be determined based on the range of capacity change, capacity change curve, volume, and other requirements.

2、 Reasonably determining the capacity and error of capacitors

The value of capacitor capacity must be selected according to the specified nominal value.

There are various error levels for capacitors. In circuits such as low-frequency coupling, decoupling, and power filtering, capacitors can have error levels of ± 5%, ± 10%, and ± 20%. However, in oscillation circuits, delay circuits, and tone control circuits, the accuracy of capacitors is slightly higher; In various filters and networks, high-precision capacitors are required to be selected.

Third: Selection of withstand voltage value

To ensure the normal operation of the capacitor, the withstand voltage of the selected capacitor should not only be greater than the actual working voltage, but also leave enough room. Generally, capacitors with a withstand voltage value more than twice the actual working voltage are selected.

Fourth: Pay attention to the temperature coefficient, high-frequency characteristics, and other parameters of the capacitor

Capacitors with low temperature coefficients should be selected for oscillation components, phase-shifting network components, filters, etc. in oscillation circuits to ensure their performance.

Introduction to SMD capacitors:

Chip capacitors, business card type stacked capacitors, are made by one-time high-temperature sintering and are also made by stacking ceramic dielectric membranes with printed electrodes (inner electrodes) in a staggered manner.

Introduction to the Internal Structure of Chip Capacitors:

Chip capacitors mainly include three parts: ceramic dielectric, inner electrode, and end electrode. The main function of ceramic dielectric is to polarize dielectric energy storage under the action of an electric field. When the polarization rate changes correspondingly when the electric field changes, the response speed and polarization rate to the electric field change are also different due to the different main polarization types of different media types.

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