Introduction
Capacitors are a fundamental component used in virtually every electronic circuit. They come in an enormous range of sizes from tiny surface mount chips just 0.2mm across to massive canisters larger than a human hand. The scale of capacitive components spans over six orders of magnitude.
But what really differs between physically small and large capacitors? This article explores in depth the key distinctions including:
- How capacitance values and applications correlate to size
- Underlying materials, construction and properties
- Performance differences like frequency response, ESR, ripple current
- Packaging and termination variations
- Cost comparisons and usage tradeoffs
- Behavior, failure modes and lifespan differences
- Comparison tables summarizing differentiating characteristics
- Real world application examples of small vs large caps
- Guidelines for selecting the optimal size capacitor
Read on to gain valuable insights into the significant differences between capacitors at opposite ends of the size spectrum.
Correlation of Size to Capacitance Value
One obvious difference between small and large capacitors is the capacitance value range:
Tiny Capacitors
- Surface mount chips below 0805 case size (2mm x 1.25mm)
- Values from low picofarads up to around 100nF
Moderate Capacitors
- Through hole axial and radial leaded caps
- Surface mounts up to 2220 case size
- Typical values from 1nF to 10uF
Large Capacitors
- Can or box styles above 25mm length
- Massive sizes over 50mm
- Range from 10uF up to thousands of farads
Higher capacitance requires larger physical size to store more charge. But it’s not all about just energy storage – construction and performance also diverge between capacitor scales.
Materials and Construction
The materials and assembly process vary significantly between differently sized capacitors:
Tiny Surface Mount Capacitors
- Multilayer ceramic capacitors (MLCC) most common
- Stacked alternating dielectric and electrode layers
- Materials like X7R, X5R, or NP0 ceramic
- Smaller case sizes are 01005 and 0201
Larger Leaded Capacitors
- Wider range of dielectric films
- Plastic films like polyester, polypropylene
- Metalized paper and oil impregnated paper
- Stacked wound or folded layers
- Aluminum can electrolytic capacitors
Massive Can Capacitors
- Aluminum electrolytic capacitors predominant
- Aluminum foil anode covered in liquid electrolyte or polymer
- Huge rolled surface area for enormous capacitance
- Sturdy cylindrical metal case for housing
Construction diverges between tiny surface mount devices up to industrial scale capacitors.
Key Performance Differences
Beyond just size and capacitance, electrical performance also differs:
Breakdown Voltage
- Tiny MLCCs: 25V to 100V common
- Leaded film caps: 250V to 630V typical
- Large can electrolytics: 450V to 550V
Maximum Ripple Current
- MLCCs: Up to around 5-10A
- Larger leaded caps: 10s to 100s of amps
- Massive can caps: Up to 500A
Frequency Response
- MLCCs effective into microwave frequencies
- Leaded caps handle RF to kHz ranges
- Electrolytics target 50/60Hz to kHz operation
Equivalent Series Resistance
- MLCCs below 100 milliohms
- Leaded caps in milliohm to ohm range
- Electrolytics from fractional to several ohms
Lifetime
- Ceramics and films over 10 years
- Electrolytics as low as 1000 hours (dependent on conditions)
Electrical performance profiles diverge based on target applications.
Packaging and Termination Styles
The wide range of capacitor sizes necessitates very different packaging approaches:
Surface Mount Multilayer Ceramic Capacitors
- Extremely compact case sizes, as small as 01005 (0.4mm x 0.2mm)
- Rectangular cuboid SMD packages solder directly to PCB
- Nickel barrier layer terminations or nickel barrier with tin or silver outer layer
- High density installation but manual rework challenging
Leaded Capacitors
- Axial cylinders with leads from both ends
- Radial caps with leads from one side
- Rigid metal tabs allow mounting holes
- Wire terminations solder into boards or connect to other components
- Manual assembly and repair
Large Can Electrolytics
- Aluminum cylindrical canister case
- Insulating plastic header seals open end
- Multiple axial wire leads connect to terminals
- Mount via brackets or straps
- Readily hand assembled but bulky footprint
Package style correlates strongly with target production volume and application environment.
Cost Scaling
In most cases, larger capacitors carry a disproportionately higher cost:
| Capacitor Class | Capacitance Range | Typical Component Cost |
|---|---|---|
| 0402 MLCC | 1nF to 1uF | $0.01 to $0.10 |
| 1206 MLCC | 1nF to 10uF | $0.05 to $0.30 |
| Radial film | 0.1uF to 1uF | $0.15 to $0.75 |
| Radial electrolytic | 1uF to 100uF | $0.20 to $2 |
| Large can electrolytic | 1000uF to 1F | $1 to $20 |
This reflects the fact that larger case sizes require more robust packaging and tolerances. However, very small 0201 and 01005 MLCCs can carry sizeable cost premiums.
Lifetime and Failure Differences
Expected usable lifetime also diverges according to capacitor size:
Tiny MLCCs
- Extremely long life of up to 200,000 hours at rated temperature
- Gradual capacitance decrease over time
- Subject to mechanical cracking and breaks
Leaded Film Caps
- Typical lifetime around 50,000 hours
- Parameter decline as materials degrade
- Drying out mechanisms in older designs
Large Electrolytic Caps
- Lifetime as low as 1000 hours at full ratings
- End of life often catastrophic short circuit
- Evaporation and drying out primary aging mechanisms
Applications determine necessary lifespan – from short term consumer devices to long duration industrial systems.
Comparison of Characteristics
Here is a summary table contrasting attributes between capacitor size classes:
| Parameter | Surface Mount MLCC | Leaded Film Cap | Large Can Electrolytic |
|---|---|---|---|
| Capacitance Range | 1pF to 0.1uF | 0.1uF to 10uF | 10uF to 10,000s uF |
| Voltage Range | 25V to 100V | 250V to 1kV | 450V to 550V |
| Temperature Range | -55°C to 125°C | -55°C to 125°C | -40°C to 85°C |
| ESR | <100 milliohm | 0.1 to 10 ohm | 0.1 to 1 ohm |
| Tolerance | +/- 1% to +/-20% | +/- 1% to +/-20% | +/- 20% to +/- 80% |
| Frequency Range | Up to GHz | Up to MHz | Up to kHz |
| Failure Mode | Cracking | Degradation | Dry out, short |
| Lifetime | Up to 200 khrs | Up to 50 khrs | 1khours to 10 khrs |
| Cost | Low | Moderate | High |
This summarizes the typical traits differentiating the classes of capacitors. Next we look at some example applications.
Application Examples
Real world scenarios help reveal appropriate size selection:
Decoupling MLCCs on CPU
The tiny 100nF decoupling capacitors must filter high frequency noise, necessitating an MLCC right at the power pins.
Snubber on Inductive Load
Snubber circuits often utilize leaded film capacitors in the nF to uF range to suppress arcs and spikes.
Power Factor Correction
Large 1000uF to 1F electrolytic capacitors are required for pole-mounted power factor correction due to their high capacitance density.
Tuned Filter Circuits
Often a combination is required – small MLCCs for bypassing and moderate leaded caps for tuning capacitance.
The application ultimately determines the performance requirements that guide capacitor size selection.
Selecting the Best Size Capacitor
Here are some principles useful in choosing the optimal size:
- Match physical size to application constraints
- Consider capacitance range needed
- Determine required voltage, current, ESR ratings
- Assess necessary frequency response
- Evaluate expected lifetime and reliability
- Weigh soldering and production constraints
- Account for vibration resistance needs
- Plan for maintenance, inspection and repair
- Analyze application cost constraints
- Select ratings with safety margin
Finding the intersection between electrical requirements, mechanical needs, manufacturing methods and cost objectives leads to an optimized capacitor sizing selection.
Frequently Asked Questions
Here are some common FAQs regarding capacitor size selection:
Q: What are pros and cons of large can electrolytic capacitors versus small MLCCs?
Electrolytics provide huge capacitance but with lower lifetime. MLCCs have superior frequency response and lifetime but much less capacitance density.
Q: What is the largest capacitance range for surface mount MLCC?
0201 and 01005 case sizes top out below 10nF but 1812 and 2220 sizes reach 0.1 to 1uF.
Q: What are key benefits of leaded capacitors?
Ease of hand assembly, measureable leads enables broader tolerance ranges, and meets high voltage requirements above SMT parts.
Q: What determines the maximum voltage ratings for capacitors?
Dielectric breakdown voltage and minimum spacing between plates sets voltage limits. Multilayer ceramic capacitors are typically <100V while film caps extend beyond 1kV.
Q: Do capacitors suffer from derating at higher temperatures?
Yes, voltage ratings are often significantly reduced at maximum rated temperatures. Always consult manufacturer datasheets.
Conclusion
While a capacitor’s fundamental purpose remains the same across all sizes, optimized construction, materials, packaging and properties for diverse applications result in major performance differences between capacitors of vastly different scales. Leveraging the detailed size comparisons presented in this article will help engineers select the optimal capacitor to fulfill the specific needs of any system.
