What are the parameters of electrolytic capacitors?

As a commonly used energy storage component in electronic circuits, the performance parameters of electrolytic capacitors directly affect the reliability and stability of circuit design. The following are the core parameters and detailed analysis of electrolytic capacitors:
1. Nominal Capacity
Definition: Refers to the ability of a capacitor to store charge, measured in microfarads (μ F) or picofarads (pF).
Scope: Common electrolytic capacitors have capacities ranging from 1 μ F to 6800 μ F, and industrial grade products can reach up to 33000 μ F.
Selection suggestion: The selection should be based on the circuit requirements. A small capacity may result in insufficient filtering, while a large capacity may increase volume and cost.
2. Rated Voltage
Definition: The maximum effective value of DC or AC voltage that a capacitor can withstand under normal operating conditions.
Scope: Common rated voltages include 6.3V, 16V, 25V, 50V, 100V, etc. Some high-voltage models can reach 700V.
Safety principle: It is recommended to choose capacitors that are 1.25 times higher than the actual working voltage to avoid the risk of breakdown caused by voltage fluctuations.
3. Operating Temperature Range
Typical values: -40 ℃ to+105 ℃, some models support -55 ℃ to+130 ℃.
Lifetime impact: For every 10 ℃ increase in temperature, the lifespan of the capacitor is reduced by about 50%; On the contrary, a temperature decrease of 10 ℃ doubles the lifespan.
4. Dissipation Factor (DF/tan δ)
Definition: Represents the proportion of energy loss of a capacitor under an alternating electric field, with lower values indicating higher efficiency.
Influencing factors:
Temperature: Tan δ is about 0.08-0.1215 at 25 ℃, and may rise to 0.15 at 125 ℃.
Frequency: Tan δ is about 0.12 at 100Hz, and may rise to 0.35 at 10kHz.
Optimization direction: The use of new electrolytes (such as quaternary ammonium salt systems) or nanocomposite dielectric films can reduce losses.
5. Leakage Current
Definition: The leakage current of an insulating medium under direct current voltage, measured in μ A.
Influencing factors:
Temperature: High temperature will intensify ion migration, leading to an increase in leakage current.
Aging: After long-term use, the electrolyte performance decreases and the leakage current may exceed the standard.
Hazard: Leakage current can cause capacitor heating, capacity decay, and even failure.
6. Lifetime
Definition: The time required for the performance of a capacitor to decay to 70% of its initial value at rated temperature and voltage.
Common specifications: 2000 hours, 5000 hours, 10000 hours.
Extension method:
Cooling: For every 10 ℃ decrease in working temperature, the lifespan is doubled.
Control ripple current: Excessive ripple current can cause internal temperature rise and accelerate aging.
7. Size and Packaging
Packaging form:
Direct insertion type: such as RB.2/. 4 (pin spacing 200mil, diameter 400mil).
Surface mount: such as 1210, 1206 (suitable for automated assembly).
Selection criteria: The selection should be based on the space and installation method of the circuit board. The direct insertion type is suitable for manual soldering, while the surface mount type is suitable for high-density design.
8. Polarity
Importance: Electrolytic capacitors have polarity, and reversing the positive and negative poles can cause short circuits or explosions.
Identification method:
Pin length: The long pin is the positive pole, and the short pin is the negative pole.
Shell marking: usually marked with "+", "-" or a color band (negative pole).
9. Equivalent series resistance (ESR)
Definition: Equivalent resistance under alternating current, affecting high-frequency performance and heat generation.
Measurement method:
Specification: Refer to the ESR value provided by the manufacturer (usually tested at a frequency of 100kHz).
Instrument measurement: Use LCR bridge or calculate through formula (ESR=Δ V/Δ I).
Optimization direction: Using low ESR capacitors can reduce ripple voltage and heat generation.
10. Ripple Current
Definition: The effective value of AC component current, influenced by temperature and frequency.
Harm: Excessive ripple current can cause internal temperature rise in capacitors and shorten their lifespan.
Selection suggestion: Choose capacitors with rated ripple current higher than the actual value according to circuit requirements.
11. Accuracy and Tolerance
Common values: ± 20%, ± 10%, and some high-precision capacitors can reach ± 5%.
Selection criteria: Select based on the accuracy requirements of the circuit for capacity, such as the filtering circuit accepting ± 20%, while the timing circuit requires higher accuracy.
The selection of electrolytic capacitors requires comprehensive consideration of nominal capacity, rated voltage, temperature range, losses, leakage current, lifespan, size, polarity, etc ESR、 Ripple current and precision parameters. In practical applications, it is necessary to balance circuit requirements (such as power filtering, coupling, decoupling) and working environment (temperature, humidity, vibration) to ensure the reliability and stability of the circuit.