The impact of capacitor failure on circuits is extensive and severe, depending on the role of the capacitor in the circuit, failure modes (open circuit, short circuit, reduced capacity, increased ESR, increased leakage current, etc.), and the design of the circuit itself. Here are some of the main impacts:
Complete open circuit failure
Filter failure (power/decoupling): This is one of the most common failure effects. Capacitors are unable to store and release charges to smooth voltage fluctuations, resulting in:
Significant increase in power ripple and noise: unstable output voltage, resulting in high-frequency spikes or low-frequency fluctuations.
Unstable operation of digital circuits: may cause microprocessor, logic chip reset, crash, data errors, or program runaway.
Analog signal quality deterioration: Introducing additional noise, reducing signal-to-noise ratio, may lead to audio distortion, video interference, etc.
Risk of damage to sensitive components: Voltage spikes may exceed the withstand voltage of subsequent components.
Coupling failure:
Signal interruption: AC signals cannot pass through, resulting in no signal input to the subsequent circuit (e.g. silent audio, no image in video).
DC bias point change: If the design relies on capacitor isolation, an open circuit may cause the DC operating point of the subsequent circuit to shift, making it unable to function properly or even damaged.
Timing/oscillation circuit failure: If the capacitor is part of an RC time constant or LC oscillation circuit, an open circuit will cause:
The oscillator stops oscillating (no output signal).
The timer time is completely incorrect or the function is malfunctioning (such as unable to delay or generate pulses).
Bypass failure: Unable to provide a low impedance path to ground for high-frequency noise or interference, resulting in noise coupling to other parts.
Complete short-circuit failure (most dangerous)
Overcurrent/burnout: A capacitor short circuit is equivalent to creating a direct, low impedance path (close to the wire) in the circuit.
Burnt fuse: If there is a fuse in the circuit, it usually blows first.
Burnt power supply: The power supply may be damaged due to overload (switching power supply may enter protection, current limiting, or burn power tubes/rectifier bridges).
Burn out wiring/pads: High current may burn out PCB wiring or pads.
Burning connected components: Resistors, inductors, or semiconductor devices (such as transistors and ICs) connected in series with short-circuit capacitors may burn out due to overcurrent.
Smoking and fire: In extreme cases, it may lead to serious safety accidents (especially for large capacity and high-voltage capacitors).
Complete loss of function: The circuit cannot function due to overcurrent protection or component damage.
DC bias point change: Forcefully flatten the voltage at both ends of the short-circuit point (close to 0V), damaging the original operating point.
Significant reduction/drying of capacity (common in electrolytic capacitors)
The filtering effect deteriorates: the energy storage capacity decreases, leading to an increase in power ripple and noise (to a lesser extent than an open circuit, but with the same trend), which affects circuit stability and may cause intermittent faults or performance degradation (such as increased audio background noise).
Weakened decoupling effect: The ability to bypass high-frequency noise decreases, and high-speed digital circuits are more susceptible to switch noise, resulting in logic errors or EMI problems.
Time constant change:
Inaccurate timing circuit: RC delay time becomes shorter, LC oscillation frequency becomes higher.
Filter characteristic changes: The cut-off frequency increases (high pass filtering passes more low frequencies, low-pass filtering attenuates more high frequencies), resulting in signal distortion.
Failure of power factor correction: In PFC circuits, a decrease in capacity can significantly reduce the effectiveness of power factor correction.
Equivalent series resistance increases (ESR increases - common for electrolytic/solid-state capacitors)
Heating: An increase in ESR due to the flow of current will generate more heat, forming a vicious cycle (temperature rise further deteriorates the capacitor), which may ultimately lead to thermal failure (bulging, spraying, open circuit).
The filtering/decoupling effect deteriorates: Even if the capacity is sufficient, the increased ESR will limit the ability of the capacitor to instantly charge and discharge current, reducing its effectiveness in suppressing high-frequency ripple and noise. Ripple voltage 'V_ripple=I2 ripple ESR', so an increase in ESR directly leads to an increase in ripple voltage.
Decreased power efficiency: More energy is dissipated in the form of heat on capacitors.
Circuit stability issue: In some feedback loops (such as switching power supply output filtering), ESR is an important factor in loop stability. An increase in ESR may disrupt the phase margin, leading to loop oscillation (manifested as low-frequency fluctuations or whistling in the output voltage).
Significant increase in leakage current
Increased power consumption: The additional leakage current path leads to unnecessary power consumption, which may cause slight heating of the capacitor.
Bias point change: In circuits that require high impedance or precision reference (such as sample and hold, input coupling of high gain amplifiers, timing capacitors), excessive leakage current will slowly change the voltage or cause the held voltage to drop too quickly.
Signal distortion: For AC coupled signals, leakage current may introduce nonlinearity or DC offset.
Summarize key impact areas
Power stability: Increased ripple noise, unstable voltage, and even power failure (short circuit).
Signal integrity: increased noise, signal distortion, attenuation, or interruption.
Circuit function: timing/oscillation error, logic error, reset, crash, complete loss of function.
Reliability/Safety: Component overheating, damage, burning, smoke and fire (risk of short circuit).
Power consumption and efficiency: unnecessary heat loss (increased ESR, leakage).
How to identify and respond
Visual inspection: There are obvious signs of failure such as electrolytic capacitor bulging, leakage, and protruding or cracked top explosion-proof valve.
Multimeter testing:
Resistance mode (after power failure): Short circuit (close to 0 Ω) or severe leakage (very low resistance). Open circuit (infinite resistance - test after discharge). Attention: Good capacitance measurement of resistance will change from low to high during the charging process.
Capacitor mode: Measure whether the actual capacity deviates significantly from the nominal value (usually by a lot).
ESR meter: It specifically measures the ESR value of capacitors and is one of the most effective methods for judging the quality of electrolytic/solid capacitors (especially when the capacity has not significantly decreased).
Oscilloscope: Directly observe whether the power ripple and signal waveform are abnormal.
Replacement method: When suspecting a capacitor failure, replace it with a new capacitor of the same specifications (note: capacity, withstand voltage, type (such as electrolytic/ceramic/film), packaging, ESR (especially important for high-frequency circuits) for testing.
Important reminder: When repairing or replacing capacitors, be sure to discharge large capacity capacitors (especially high-voltage capacitors in switch mode power supplies, CRT displays, and audio amplifiers) first to prevent electric shock hazards! Short circuit the two poles of the capacitor for a few seconds using well insulated wires or specialized discharge devices. safety first!