1. Core Structure and Working Principle

• Core Construction: Inside, it consists of an anode aluminum foil (with an etched surface to increase area, forming an aluminum oxide dielectric layer), electrolyte (the conductive medium), a cathode aluminum foil, and separator paper, all wound together and sealed in an aluminum casing.

  
  

• The "Snap-in" Design: Its most distinctive visual feature is the two bolt-like terminals made of copper or aluminum. This design is not for aesthetics but to meet the requirements for high current-carrying capacity. The bolt structure allows for easy, secure, and low-impedance connection to the PCB's copper foil or busbar using nuts and washers, effectively reducing contact resistance and heat generation—something that pin-soldering methods of smaller components cannot match.

  
  

• Performance Characteristics: They typically feature high capacitance (from hundreds of µF to tens of thousands of µF), high voltage ratings (from tens to hundreds of volts), high ripple current handling capability, and long service life. The top of the casing usually has a pressure relief vent (marked with a "K" or cross score), which ruptures in a controlled manner if internal pressure builds up due to failure, preventing the casing from exploding.

  
  

2. Primary Functions and Application Areas

1. Filtering and Smoothing: This is their core function. After rectifying alternating current (AC) to direct current (DC), the voltage contains ripple. Snap-in capacitors are connected in parallel across the DC bus. They utilize their charge/discharge characteristics to absorb this ripple, delivering a smooth, stable DC voltage, providing "clean" power to subsequent circuits.

   
   

2. Energy Buffering and Transient Response: When the load changes suddenly (e.g., motor startup, instantaneous power surge), the power supply may not respond immediately. The energy stored in the snap-in capacitor can be released rapidly to bridge this instantaneous power gap, stabilizing the system voltage and preventing equipment resets or malfunctions.

   
   

3. Harmonic and Noise Absorption: In switched-mode power circuits like frequency converters and inverters, the high-speed switching of power devices generates high-frequency noise and harmonics. Snap-in capacitors provide a low-impedance path to absorb this interference, preventing it from affecting the control system and surrounding equipment.

   
   

• Industrial Frequency Converters & Servo Drives: Used for DC bus filtering, they are key components ensuring stable and efficient operation of drive systems.

  
  

• Uninterruptible Power Supplies (UPS) & Telecom Power Supplies: Serve as core components for energy storage and filtering.

  
  

• New Energy Sector: Photovoltaic inverters, wind power converters, motor drives, and onboard chargers (OBC) for new energy vehicles.

  
  

• Industrial Power Supplies & Welding Equipment: Provide stable, high-power DC output.

  
  

3. Key Points for Selection and Use

• Rated Voltage: Must be higher than the maximum possible DC voltage in the circuit, with a safety margin (typically 1.2 to 1.5 times).

  
  

• Rated Capacitance: Determined by calculation based on system power, ripple current requirements, and holdup time needs. Higher capacitance offers better filtering but increases size and cost.

  
  

• Rated Ripple Current: The maximum RMS alternating current the capacitor can withstand at its maximum operating temperature. This is a key indicator of its performance in high-frequency switching environments. During selection, it is mandatory to ensure the actual ripple current is below the capacitor's rated value; otherwise, overheating will drastically shorten its lifespan.

  
  

• Operating Temperature & Lifetime: Usually specified in a form like "105°C, 2000 hours." The actual lifetime is highly dependent on operating temperature, roughly following the rule of "lifetime doubles for every 10°C decrease in temperature." Therefore, good thermal layout significantly enhances capacitor and overall system reliability.

  
  

• ESR (Equivalent Series Resistance): A lower ESR means lower power loss and self-heating in the capacitor, leading to better high-frequency performance.

  
  

1. Observe Polarity: Electrolytic capacitors have positive and negative terminals. Reverse connection can cause a short circuit, leading to rapid heating, bulging, or even explosion.

   
   

2. Maintain Safe Distance: Ensure adequate spacing from heat-generating components (e.g., heat sinks, power resistors) to avoid exposure to high temperatures.

   
   

3. Proper Torque: Use a torque wrench to fasten the terminal bolts according to the specification sheet's required torque. This ensures good contact without over-tightening, which could damage the terminals or PCB.

   
   

Conclusion