CBB Capacitor: Types, Specifications and Selection Guide

INTRODUCTION

CBB capacitors represent one of the most widely used capacitor technologies in industrial electronics, AC mains filtering, motor circuits, and power-factor correction systems. Yet many OEM engineers lack a clear understanding of CBB variants, performance specifications, and proper selection criteria. This confusion leads to specification errors, thermal failures, and costly field replacements.

CBB is a category designation defined under GB/T 2470 (formerly GB 2470-1981), the Chinese standard for fixed capacitor type naming. It refers to metallized polypropylene film capacitors in Chinese industry nomenclature, and encompasses multiple specific series (e.g., CBB22, CBB60, CBB65). CBB capacitors are widely available across Asian supply chains and are commonly specified for applications requiring reliable AC filtering and good thermal stability.

This article explains CBB fundamentals, clarifies variant differences, and provides practical selection guidance.

WHAT ARE CBB CAPACITORS?

Technology Basics

CBB follows the type-naming rules of GB/T 2470 (formerly GB 2470-1981), the Chinese standard for fixed capacitor type naming. The core technology is straightforward: a thin aluminum layer is vacuum-deposited directly onto polypropylene film, which is then wound into a cylindrical package and encapsulated.

Key characteristics:

• Excellent frequency response (good to several MHz)
• Very low dissipation factor (typically ≤0.1–0.2% at 1 kHz, depending on series)
• Extremely low leakage current (well below 1 µA per µF in typical parts; confirm against datasheet)
• Self-healing capability against transient surges
• Long storage life (excellent charge retention)
• Temperature-dependent voltage derating

CBB and MKP are tightly linked: MKP is the universal technical abbreviation for metallized polypropylene film capacitors, while CBB is the Chinese series designation under GB/T 2470. That means CBB21, CBB22 and CBB X2 all fall into the MKP family.

The practical distinction comes from certification, construction and intended use. X2 safety-rated capacitors (a subset of MKP / CBB) are designed for mains EMI filtering and must pass strict IEC 60384-14 safety tests. CBB22 is commonly specified for oscillation, coupling, and capacitive dropper circuits.

CBB22 may serve as a lower-cost alternative to imported MKP components only when voltage, pulse and safety requirements are fully matched. Standard CBB22 parts are not X2 safety certified and usually carry a lower voltage withstand margin than X2-rated variants.

For reference: CBB21 is the general-purpose non-safety MKP type; CBB X2 corresponds to X2 safety-certified MKP capacitors. (Note: MKP41 is a specific WIMA product series, not a generic X2 designation.)

Self-Healing Mechanism

When voltage stress causes localized dielectric breakdown in CBB, the thin aluminum electrode at that location vaporizes, isolating the fault. The capacitor remains operational but loses a small amount of capacitance.

Advantage: A single transient surge does not immediately destroy the component.

Limitation: Repeated self-healing events accumulate electrode loss, gradually reducing capacitance. In extreme cases, thermal energy can trigger cascading failures.

Critical point: Self-healing is NOT failsafe protection. System-level surge protection remains essential.

Need Help Selecting a CBB Capacitor?

Selecting a CBB capacitor involves more than matching capacitance and voltage. Operating temperature, ripple current, frequency, safety classification, mounting conditions, and expected service life should also be considered.

LCA supports engineers and purchasing teams with CBB capacitor selection based on actual application requirements.

Send us your required capacitance, voltage, operating temperature, ripple-current conditions, dimensions, and application information. Our engineering team can review the requirements and recommend a suitable configuration.

CBB VARIANTS: CBB21, CBB22, AND CBBX2

CBB21: General-Purpose Film Capacitor

CBB21 is a metallized polypropylene film capacitor for general DC and AC applications. Typical DC voltage ratings span 100 V to 1000 V, with capacitance values from 0.01 µF to 3.3 µF . The operating temperature range is –40°C to +105°C, with a rated temperature of 85°C.

Voltage derating: From +85°C to +105°C, the rated DC voltage typically decreases by 1.25% per°C, referenced to the 85°C rating.

Applications: DC filtering, coupling, and general-purpose circuits. CBB21 and CBB22 share nearly identical construction and are often treated as the same family in supplier documentation .

CBB22: Similar Construction, Minimal Technical Distinction

CBB22 uses the same metallized polypropylene film construction as CBB21. Typical DC voltage ratings include 250 V, 400 V, 630 V, and higher, with capacitance ranges from 0.01 µF to 3.3 µF . The temperature range is also –40°C to +105°C .

Key point: CBB21 and CBB22 are frequently listed together by manufacturers, as the technical differences between them are minimal. The “dual-voltage” distinction sometimes attributed to CBB22 is not a standardized specification; actual AC/DC ratings should be confirmed against the specific manufacturer’s datasheet .

CBBX2: Safety-Rated Mains Suppression

CBB X2 carries the X2 safety classification under IEC 60384-14 and is designed for direct connection across AC mains, subject to proper circuit topology and overcurrent protection.

Key requirements:

• Rated voltage: 275 V AC, 305 V AC, or 310 V AC (50/60 Hz)
• Impulse withstand: 2500 V peak (the mandatory X2 impulse test per IEC 60384-14)
• Temperature range: –40°C to +110°C (climatic category 40/110/56)
• Voltage derating: From +85°C to +110°C, DC voltage typically derates at 1.25% per °C
• Discharge requirement: End-equipment safety standards generally require X capacitors above 300 nF to discharge to a safe voltage (typically <60 V) within 1–2 seconds after power removal; many X2 parts include an integrated discharge resistor

Applications: EMI suppression at AC mains inlet, industrial equipment filtering, safety-critical systems.

Cost: Premium over non-safety CBB variants due to safety certification and testing requirements.

THERMAL DERATING: CRITICAL FOR SELECTION

CBB capacitor voltage rating applies at the rated temperature of +85°C (not 20°C or 25°C). At temperatures above +85°C, usable voltage decreases according to the manufacturer’s derating curve.

Typical derating for CBB21/CBB22: From +85°C to +105°C, the rated DC voltage decreases by 1.25% per °C (some series specify 1.5%/°C), referenced to the 85°C rating.

Example calculation:

• Capacitor rated 250 V DC at 85°C
• Operating temperature: 105°C (20°C above the 85°C reference)
• Derating at 1.25% per °C: 250 V × (1 − 0.0125 × 20) = 250 V × 0.75 = 187.5 V usable at 105°C

This represents a 25% reduction at 105°C — meaningful, but far less dramatic than the 60% figure that would result from incorrectly applying derating from 25°C. Always apply the derating curve from the specific supplier datasheet. Never assume the nameplate voltage applies at temperatures above the rated temperature.

RIPPLE CURRENT: THERMAL STRESS

Ripple current (AC component superimposed on DC or AC voltage) creates heat in the capacitor: P = I²_RMS × ESR.

Critical warning: Exceeding the ripple-current rating results in excessive internal heating. Unlike aluminium electrolytic capacitors, where rising temperature raises ESR and may trigger self-reinforcing thermal runaway, CBB film capacitors show slightly falling or flat ESR as temperature increases. They do not form the same fast positive-feedback loop. Even so, operation beyond the ripple rating still causes excessive temperature rise, which accelerates ageing (capacitance drift, gradual ESR rise), degrades the dielectric, and under sustained extreme overstress may lead to thermal failure or fire.

The primary risk for CBB capacitors is not fast, seconds-scale thermal runaway, but accelerated long-term degradation. Repeated self-healing events under heavy ripple stress slowly increase ESR over service life, which further raises heat dissipation. This creates a gradual degradation loop instead of an instantaneous catastrophic cascade.

Always verify actual ripple current in your circuit and select a capacitor rated above that requirement. Include 20–30% design margin for worst-case conditions.

CBB APPLICATIONS IN PRACTICE

AC Mains EMI Filtering (CBBX2)

CBB X2 capacitors suppress conducted EMI generated by switching power supplies connected to AC mains. A typical topology is an LC filter, with the CBB X2 capacitor connected across the AC mains line, paired with a series inductor and damping resistor.

Thermal stress: The capacitor carries ripple current consisting of the 50/60 Hz fundamental plus high-frequency harmonic currents from the switching converter. CBB X2 must be rated for this combined continuous RMS current.

Safety requirement: X2 rating mandatory. Bleed resistor ensures safe discharge after power removal (critical for personnel safety during maintenance).

Motor Circuits (CBB60/CBB61/CBB65, not CBB21/22)

Motor-run capacitors are typically dedicated series such as CBB60, CBB61, or CBB65, not the general-purpose CBB21/CBB22. They improve efficiency and power factor in single-phase motor circuits. Standard motor-run capacitors often have a maximum operating temperature of +70°C to +85°C .

Design consideration: If the internal temperature inside the motor housing exceeds the capacitor’s rated temperature, voltage derating applies. Note that the 1.25%/°C derating factor quoted earlier for CBB21/CBB22 is only an example; the actual derating curve must be taken from the datasheet for the specific motor-run series. For illustration, a 480 V capacitor following 1.25%/°C derating above 85°C would deliver approximately 360 V usable voltage at 105°C.

Power-Factor Correction (PFC)

PFC systems use CBB capacitors to reduce reactive power and improve power factor in industrial installations. Capacitors experience continuous ripple current at fundamental frequency (50/60 Hz) plus harmonic currents from nonlinear loads.

Ripple-current calculation: Must account for both fundamental and harmonic components. Actual RMS current often exceeds simple estimates.

SELECTION CHECKLIST

Step 1: Define voltage requirements

• Identify maximum AC or DC voltage capacitor will experience
• Apply temperature derating for operating temperature
• Select voltage class 1 step above calculated requirement

Step 2: Select CBB variant

• General-purpose DC/AC filtering, coupling, oscillation → CBB21 or CBB22 (nearly identical; confirm specific series datasheet)
• Direct AC mains connection (line-to-line, EMI suppression) → CBBX2 (X2 safety-rated, IEC 60384-14; never substitute a non-X2 type in this position)
• Motor-run circuits → dedicated series (CBB60/CBB61/CBB65), not CBB21/22

Step 3: Calculate capacitance

• Determine required capacitance from circuit topology
• Verify frequency response adequate for application

Step 4: Verify ripple current

• Estimate actual RMS ripple current
• Select capacitor rated above estimated current
• Include 20–30% safety margin

Step 5: Confirm compliance

• Request technical datasheet with derating curves
• Verify thermal cycling and environmental testing
• Confirm compliance with relevant standards (IEC 60384-14 for X2, etc.)

Frequently Asked Questions

Q: How does CBB differ from MKP capacitors?

CBB and MKP both refer to metallized polypropylene film capacitors under different naming standards: MKP uses IEC terminology while CBB is a Chinese series designation, and both can be general-purpose or X2-certified. CBB22 is commonly used for oscillation, coupling and capacitive dropper circuits and may replace non-certified MKP for cost savings only when voltage and reliability requirements are met; the 2000 VDC / 2s withstand test is an IEC 60384-14 X2 certification requirement rather than inherent to MKP, and standard CBB22 only undergoes a ~1.6× rated voltage dielectric test without X2 surge approval, so selection depends on application and certification needs.

Q: Is CBBX2 safe for all mains applications?

No. X2 rating ensures capacitor can survive surge stress and thermal cycling, but proper circuit design remains essential. Direct mains connection requires appropriate overcurrent protection, proper filter topology, and bleed resistor for safe discharge. X2 rating is necessary but not sufficient for safe operation.

Q: Can self-healing protect against repeated surges?

Self-healing handles occasional transient surges. However, repeated events accumulate electrode loss and degrade capacitance. In harsh industrial environments with frequent surges, rely on system-level surge protection, not capacitor self-healing alone.

Q: What ripple current should I use for design?

Actual RMS ripple current through the capacitor, accounting for all frequency components (fundamental, harmonics, switching frequencies). Conservative design: calculate theoretical requirement, then add 20–30% margin. Request from supplier: capacitor rated above calculated ripple current. Verify at maximum operating temperature.