Polymer capacitors (mainly referring to solid-state polymer electrolytic capacitors) are widely used in modern electronic devices due to their excellent high-frequency performance and stability. The following are its key parameters, original compilation and classification explanation:
1、 Basic electrical performance parameters
Nominal capacitance (C)
Unit: microfarads (μ F)
Definition: The capacitance value measured at a specified frequency and temperature.
Characteristics: Wide capacitance range (1 μ F~1000 μ F+), but the capacitance value is usually lower than that of liquid electrolytic capacitors under the same volume.
Rated voltage (V_R)
Unit: Volt (V)
Definition: The highest DC voltage that can be continuously applied.
Scope: Common 2.5V~100V, high voltage models can reach 250V
Attention: Leave a margin (such as using 80% derating) to avoid overvoltage failure.
Equivalent series resistance (ESR)
Unit: milliohms (m Ω)
Core advantage: 10-100 times lower than liquid electrolytic capacitors (can be as low as 5m Ω).
Impact:
Directly determine the ripple current capability;
Affects the efficiency of high-frequency filtering (the lower the ESR, the smaller the high-frequency loss).
Ripple current (I2 Ripple)
Unit: Ampere (A RMS)
Definition: The maximum effective value of AC current allowed to pass through a capacitor.
Key points:
Determined by ESR and heat dissipation capability (the lower the ESR, the larger the I2 Ripple);
Low attenuation at high temperatures (better than liquid electrolytic capacitors).
Impedance frequency characteristics (| Z |)
Features: Maintain low impedance in a wide frequency range (such as 100kHz~1MHz), suitable for high-frequency switching power supply filtering.
2、 Reliability and lifespan parameters
Working temperature range (TOP)
Common: 55 ℃~+105 ℃ or 55 ℃~+125 ℃.
High temperature advantage: Polymer materials have no electrolyte drying problem and a longer lifespan.
Rated lifespan
Unit: Hour (h)
Definition: Expected lifespan at rated temperature (such as 105 ℃) and rated voltage (commonly 2000h~10000h).
Lifetime calculation: Following the Arrhenius formula, the lifespan doubles for every 20 ℃ decrease in temperature.
Formula: ` L_actual=L_rated × 2 ^ [(Ttrated_actual)/20]`
Failure rate (FIT)
Unit: number of failures per 10 ^ 9 hours
Characterize long-term reliability, typically<50 FIT.
3、 Physical and structural parameters
Tolerance
The allowable deviation of nominal capacity is commonly ± 20% (wider than ceramic capacitors).
Leakage current (I2 Leakage)
Unit: microampere (μ A) or percentage of CV value (capacitance x voltage).
Characteristics: Lower than liquid electrolytic capacitors (usually<10 μ A or 0.01CV).
Temperature coefficient
The capacitance value of polymer capacitors varies less with temperature (better than X5R/X7R ceramic capacitors).
Size and packaging
Patch type: Common EIA standards (such as 1210, 1812).
Lead type: radial or axial pin.
Volume efficiency: smaller than liquid electrolytic capacitors, but with a lower capacitance voltage product than ceramic capacitors.
4、 Special characteristics
Bipolar design (BiPolar)
Some polymer capacitors can withstand reverse voltage (usually 10%~15% of rated voltage) and are used in AC circuits.
Failure mode
Safety failure: During a short circuit, the polymer layer vaporizes, increasing resistance (open circuit failure) and making it less prone to fire and explosion (key safety advantage).
Summary of Selection Points
|Parameters | Advantages of Polymer Capacitors | Design Focus|
|ESR | Extremely low (m Ω level) | High frequency ripple suppression, efficiency improvement|
|Ripple current | High (ESR low+high temperature resistance) | Power input/output filtering capability|
|Long lifespan (no electrolyte drying) | Reliability in high temperature environments|
|Failure safety | Open circuit failure (safety) | High reliability system requirements|
|Size | Smaller than liquid electrolytic capacitors | Space limited scenarios|
Typical application scenarios
Switching power supply output filtering (CPU/GPU power supply)
High frequency DCDC converter
Decoupling of low-noise analog circuits
Replace tantalum capacitors (to avoid the risk of ignition failure)
Attention: Polymer capacitors have lower voltage and capacity limits than liquid electrolytic capacitors, and are more expensive. The selection needs to balance performance, size, cost, and reliability requirements.
