Capacitor Derating: Voltage, Temperature and Category Limits

Capacitor derating means operating a capacitor below specified electrical or temperature limits to provide appropriate design margin. This article explains capacitor voltage derating, category voltage, temperature and surge-current considerations, and shows design and component engineers how to combine these requirements without overlooking manufacturer-specific restrictions.

Key Takeaways

Derating is a technology-specific selection process, not a universal percentage to apply to every capacitor.

Distinguish rated voltage, temperature-dependent category voltage and the manufacturer’s recommended application voltage.
Use the most restrictive independent voltage limit, but multiply ratios when the manufacturer applies an application margin to an already reduced category voltage.
Check peak terminal voltage, ripple-current heating, polarity and startup transients as well as steady DC voltage.
MnO₂ tantalum and polymer tantalum capacitors require different guidance; percentages cannot be transferred automatically between cathode systems or product series.
For non-solid aluminium electrolytic capacitors in filtering service, temperature and ripple heating are often more important lifetime factors than reducing an already permissible DC voltage.
For Class II MLCCs, verify usable capacitance under DC bias separately from voltage-rating compliance.

Capacitor Derating: Principles and Limits

The reasons for derating differ between capacitor technologies. They include reducing dielectric stress, improving reliability, controlling temperature rise, limiting vulnerability to startup events and maintaining the electrical parameters required by the circuit. A single percentage does not address all of these mechanisms. [1–5] Voltage and temperature are the most commonly discussed derating parameters, but ripple current, available surge current and the thermal environment also matter. For signal coupling and timing circuits, leakage and parameter stability may dominate; for power supplies and SMPS input or output filtering, ripple losses and startup conditions require particular attention. Figure 1 preserves an example of a polymer tantalum derating chart. Such charts illustrate the relationship between voltage and temperature, but the applicable product datasheet and application instructions determine the limits for a particular design.

Example voltage and temperature derating chart for polymer tantalum capacitors — Figure 1. Polymer tantalum capacitor derating example chart; source: KEMET Electronics. Use the applicable product documentation for component selection.

Category Concepts and Derating

Voltage derating normally means using a capacitor below a stated voltage reference. Always identify that reference: a percentage of rated voltage is not necessarily the same as the same percentage of category voltage at the operating temperature. [1–3]

Voltage derating and operating ratio

In this article, d is the dimensionless fraction subtracted from the reference voltage V_ref, and V_allow is the resulting allowable application voltage. Eq. (1) defines the convention; voltages are expressed in volts.

V_{\mathrm{allow}} = (1-d)V_{\mathrm{ref}} \tag{1}

For example, 20% derating means an operating ratio of 80%. Applied to a 10 V reference, Eq. (1) gives an allowable voltage of 8 V. If one independent limit requires 20% reduction from rated voltage and another requires 30% reduction from the same rated voltage, the 30% reduction is more restrictive. This example does not establish how a manufacturer combines category-voltage reduction with a separate reliability margin.

For an ideal capacitor with voltage-independent capacitance, stored energy E in joules depends on capacitance C in farads and terminal voltage V in volts, as shown in Eq. (2). [4]

E = \frac{1}{2}CV^{2} \tag{2}

Reducing voltage therefore reduces stored energy when capacitance remains constant. However, stored energy alone is not a reliability or lifetime model, and Eq. (2) should not be used with a fixed nominal capacitance to describe strongly voltage-dependent Class II MLCC behaviour.

High operating temperature and category voltage

Rated voltage V_R applies under the conditions specified by the manufacturer. Category voltage V_C(T) is the permitted voltage at temperature T where the documentation defines a temperature-dependent operating limit. The upper category temperature T_UC identifies the upper temperature boundary under the specified conditions; it does not mean that full rated voltage is available throughout the temperature range. [1–3]

Figure 2 illustrates the category concept. Read the temperature breakpoints and permitted voltage from the selected product documentation rather than assuming that all technologies share the same curve.

Illustration of capacitor voltage derating towards the upper category temperature — Figure 2. Typical voltage derating at the upper category temperature. The applicable voltage and temperature relationship is product-specific.

For example, Vishay describes several conventional MnO₂ tantalum families whose maximum working voltage begins decreasing above 85 °C towards approximately two-thirds of rated voltage at 125 °C. Individual rating tables can use rounded category voltages, so the table value takes precedence over a generic fractional approximation. Other series have different limits. [2, 3]

The expression temperature derating can refer either to reducing permitted electrical loading as temperature rises or to choosing an operating temperature below the component’s maximum. State which meaning applies. Neither a lower voltage nor a lower ripple current permits operation beyond an explicitly specified temperature boundary.

DC operation, ripple current and internal heating

An ideal capacitor draws no steady current after charging from a constant DC source. A real capacitor can dissipate power through leakage, and DC-biased capacitors in power circuits commonly carry substantial AC ripple current. It is therefore incorrect to assume that a capacitor used on a DC rail produces no internal heating. [4]

For a single ripple-frequency component, Eq. (3) estimates internal dissipation P_loss in watts from RMS ripple current I_rms in amperes, equivalent series resistance ESR in ohms, DC voltage V_DC in volts and leakage current I_leak in amperes. [4]

P_{\mathrm{loss}} \approx I_{\mathrm{rms}}^{2}\,\mathrm{ESR} + V_{\mathrm{DC}}I_{\mathrm{leak}} \tag{3}

Use ESR at the relevant frequency and temperature. When the waveform contains significant harmonics, account for the loss contribution at each frequency using the manufacturer’s method. Check local ambient temperature, self-heating and the specified temperature measurement basis; enclosure air temperature alone may not represent the capacitor’s operating condition. [3, 4]

Surge-current load limitation

Solid tantalum capacitors require particular attention to charging transients, source impedance and available fault current. Low-impedance connections to a battery or a DC/DC converter input can impose different startup stresses from a current-limited timing or coupling circuit. Excessive stress can cause dielectric breakdown and destructive failure, especially with MnO₂ cathode systems. [1, 2]

A higher voltage rating can provide additional dielectric margin, but it does not independently establish an acceptable surge-current capability. Assess the complete startup waveform, any series impedance or current limiting, and the manufacturer’s conditions for the selected component. [1, 2]

MnO₂ tantalum: Vishay commonly recommends application voltage around 50% to 60% of rated voltage under its stated conditions, with more conservative treatment for some higher-voltage ratings. A blanket 20% reduction for every non-surge application is not an appropriate general rule. [1, 2]
Polymer tantalum: Vishay’s cathode-system guidance describes 10% reduction for ratings up to and including 10 V and 20% for ratings above 10 V. These are manufacturer recommendations, not universal approval for every circuit or temperature. Its temperature-dependent recommended-voltage curves must also be observed. [1]
Do not treat a surge-voltage test rating as additional continuous operating headroom. Test duration, repetition, temperature and circuit impedance are part of the specified duty. [2, 3]

Reliability improvement and lifetime

Reducing applied voltage can substantially reduce dielectric stress and improve tantalum capacitor reliability. However, failure-rate predictions, startup-survival assessment and wear-out lifetime are different evaluations. A favourable steady-state reliability calculation does not establish immunity to a damaging turn-on event. [1, 2]

For non-solid aluminium electrolytic capacitors in ordinary filtering service, ambient temperature and ripple-current heating are often the dominant lifetime factors. Nippon Chemi-Con explains that reducing voltage below rating can have little lifetime effect for many products, although voltage is included in the models for certain larger, higher-voltage constructions. Use the series-specific lifetime model and its extrapolation limits. [4]

Film capacitors likewise require the selected manufacturer’s voltage, temperature, AC-loading and pulse-duty information rather than a lifetime rule borrowed from tantalum or aluminium electrolytic technology. Derating is not evidence of a particular service life unless supported by the applicable model and operating conditions.

Use reliability terminology carefully: improved reliability generally means a lower failure rate and, where the model supports it, a higher mean time between failures, MTBF. MTBF is not a wear-out lifetime or a guaranteed replacement interval.

Electrical parameter stability in MLCCs

Class II multilayer ceramic capacitors, including X5R and X7R types, use high-permittivity ferroelectric materials commonly based on BaTiO₃. Their effective capacitance can decrease under DC bias. Compliance with the voltage rating therefore does not establish that the nominal capacitance is available in the circuit. Class I temperature-compensating types such as C0G do not exhibit the same ferroelectric DC-bias characteristic. [5]

Reducing applied DC voltage can recover usable capacitance, but the result depends on the exact component. Compare manufacturer bias curves and check temperature, AC measurement amplitude and ageing where relevant. Do not assume that selecting a higher voltage rating automatically guarantees the required effective capacitance. [5]

Ferroelectric MLCCs can also expand and contract under varying voltage, transferring vibration to the PCB and producing audible noise. Reducing electrical excitation may help, but the waveform and mechanical coupling also matter. Murata does not regard this acoustic phenomenon itself as a reliability problem for the capacitor or neighbouring components; noise-sensitive equipment still requires functional assessment. [6]

Combining Derating Requirements

The original question behind multiplying derating requirements is important: must the designer use the largest percentage, or apply more than one reduction? The answer depends on the reference voltage and the manufacturer’s instructions.

Independent limits: use the lowest allowable voltage

If several requirements independently specify complete allowable voltages V₁, V₂ and subsequent limits in volts, the application must satisfy all of them. Eq. (4) selects the lowest allowable voltage.

V_{\mathrm{allow}} = \min\left(V_{1},V_{2},\ldots\right) \tag{4}

This is the limited situation in which “use the greater derating percentage” works: each percentage must describe an independent limit relative to the same reference. It does not remove separate ripple-current, temperature, polarity or surge-current restrictions.

Application ratios referenced to category voltage

Some documentation instead specifies an application ratio k_app relative to category voltage. If k_T(T) is the ratio of category voltage to rated voltage at temperature T, the two dimensionless ratios combine as shown in Eq. (5). [1, 3]

V_{\mathrm{allow}}(T) = k_{\mathrm{app}}V_{\mathrm{C}}(T) = k_{\mathrm{app}}k_{T}(T)V_{\mathrm{R}} \tag{5}

Vishay’s COTS tantalum guidance explicitly states that above 85 °C the recommended ratio is applied with respect to category voltage. Its polymer cathode-system chart also distinguishes the category-voltage boundary from the lower recommended application-voltage curves. Neither arrangement is represented by simply discarding the smaller percentage. [1, 3]

For a two-thirds category-voltage ratio and an 80% application ratio, the allowable voltage is approximately 53.3% of rated voltage. With a 50% application ratio, it is approximately 33.3%. These are illustrative calculations; use the actual category-voltage table and recommended operating curve when selecting a part.

Worked Example: A 12 V DC/DC Converter Input

Consider the original example: a nominal 12 V converter input, candidate 16 V tantalum capacitors, and maximum operating temperatures of 105 °C or 125 °C. The calculations below retain the original voltage choices while distinguishing arithmetic under stated assumptions from a valid component approval.

For the arithmetic only, take 12 V as the maximum applied voltage. A real design must replace this assumption with the worst-case terminal waveform, including supply tolerance, ripple, startup overshoot and other relevant transients. Also establish the capacitor temperature rather than using the equipment temperature without accounting for local heating. [2–4]

Polymer tantalum at 105 °C

If the selected polymer series permits an application voltage of 80% of rated voltage at 105 °C, a 16 V component allows 16 × 0.80 = 12.8 V. It passes the simplified 12 V voltage check with 0.8 V remaining to that recommended limit. This does not establish adequate margin for the actual supply waveform, ripple heating or startup conditions. [1]

Polymer tantalum at 125 °C

Under the original assumption that a 33% category reduction and a 20% application reduction are independent limits referred to rated voltage, the more restrictive limit is 16 × 0.67 = 10.72 V, or approximately 10.7 V. The original rejection of a 16 V part is therefore arithmetically correct under that assumption.

The original next step, selecting 20 V, is not generally valid. If the manufacturer applies the 80% application ratio to a category voltage of two-thirds of rated voltage, Eq. (5) gives approximately 8.53 V for a 16 V part, 10.67 V for a 20 V part and 13.33 V for a 25 V part. In this illustrative case, 25 V is the first of those three ratings to pass the simplified 12 V check. Actual acceptance depends on the selected series’ recommended curve and remaining waveform margin. [1]

MnO₂ tantalum in a surge-sensitive input circuit

With a 50% application ratio referred to rated voltage, the original result is 16 × 0.50 = 8 V, so a 16 V part does not pass. A 25 V part gives 12.5 V and passes the simplified voltage check only under the conditions where that ratio applies. Vishay’s guidance includes a 25 V recommendation for a 12 V rail below 85 °C. [2]

That result cannot be extended unchanged to 105 °C or 125 °C. Where the same 50% ratio is applied to category voltage, the reduced category value must be used. For example, Vishay’s COTS table lists 17 V category voltage for a 25 V rating at 125 °C. Applying 50% gives 8.5 V, not 12.5 V. The original 25 V selection is therefore not adequate under that documented rule at 125 °C. [3]

Moving a capacitor to a converter output, coupling or timing position does not automatically justify a universal 20% reduction. Review the actual source impedance, transient exposure, temperature and component guidance for that circuit. [1–3]

Design and Selection Checklist

Document the operating conditions and the source of each limit before approving a capacitor or an alternative part. Derating should produce a traceable design decision, not just a percentage entered in a spreadsheet.

Application and waveform: identify signal, timing, decoupling, power filtering or pulse service; record the worst-case voltage waveform, polarity, startup and repetitive transient conditions.
Voltage references: record rated voltage, category-voltage values, temperature breakpoints and recommended application curves. State explicitly whether each ratio refers to rated voltage or category voltage.
Thermal loading: compare ripple current at the applicable frequency and temperature; check ESR, cooling assumptions, self-heating and the manufacturer’s temperature limits. [3, 4]
Usable capacitance: include initial tolerance and relevant bias, temperature, frequency and ageing effects. For Class II MLCCs, use the exact part’s characteristic data. [5]
Reliability and lifetime: distinguish wear-out estimates from failure-rate calculations and startup validation. Use the applicable series model within its stated range. [1, 4]
Catalogue versus custom: select a catalogue part only within its documented conditions. If the required waveform, temperature or lifetime is outside that coverage, obtain an agreed manufacturer specification rather than extrapolating a generic rule.
Qualification and safety: verify the qualification evidence, assembly restrictions and approvals required for the equipment. Voltage margin does not replace safety classification or assessment of short-circuit, venting and fire consequences. [2–4]
Purchasing and substitution: approve the complete ordering code, including construction and cathode system where relevant. Do not treat matching capacitance, voltage and package as proof of equivalent derating behaviour.
Validation: measure terminal voltage and temperature under relevant operating extremes and startup conditions. Retain the calculation assumptions, manufacturer documents and validation results with the design record.

Conclusion

Capacitor derating starts by identifying the relevant voltage reference, operating temperature and physical stress mechanism. Use the lowest independent allowable voltage, but apply combined ratios when the manufacturer references an application margin to category voltage.

A component passes selection only when its actual voltage waveform, surge exposure, ripple heating, usable capacitance and required service performance satisfy the applicable product guidance. A nominal voltage rating or a familiar percentage is not sufficient on its own.

FAQ

These questions address common interpretation and selection problems when applying capacitor derating.

What does 20% capacitor voltage derating mean?

In this article, 20% derating means subtracting 20% from the stated reference voltage and operating at no more than 80% of that reference. A 10 V reference therefore gives 8 V. Check whether the manufacturer uses rated voltage or temperature-dependent category voltage as the reference before calculating the allowable application voltage.

Should voltage and temperature derating factors be multiplied?

Multiply them when the manufacturer applies an application-voltage ratio to an already reduced category voltage. If the requirements instead define independent allowable voltages, use the lowest of those limits. There is no universal rule that the largest percentage alone covers every requirement. Identify the reference voltage and follow the selected product documentation.

What is capacitor category voltage?

Category voltage is the permitted voltage at a specified temperature where the manufacturer defines a temperature-dependent operating limit. It may be lower than rated voltage near the upper category temperature. A separate recommended application margin may also apply. Read the voltage table and operating curves for the exact series rather than assuming one universal temperature relationship.

Do all tantalum capacitors need 50% voltage derating?

No. Recommendations differ between MnO₂, conductive polymer and other tantalum constructions, and also depend on product series and operating conditions. MnO₂ guidance commonly uses more conservative voltage ratios than polymer guidance. Check temperature-dependent application limits, source impedance, startup transients and ripple heating rather than transferring a percentage from another cathode system or circuit.

Does voltage derating guarantee capacitor lifetime or usable capacitance?

No. Lifetime depends on the technology and operating conditions, including temperature and ripple heating. Class II MLCC capacitance can also fall under DC bias even when voltage remains below rating. Use the applicable manufacturer lifetime model and exact-part capacitance data, then validate the selected component under the intended electrical and thermal conditions.

How to Apply Capacitor Derating in Design

Follow this procedure to turn product limits and application requirements into a documented component-selection decision.

A procedure for selecting and validating capacitor derating limits.

Identify the capacitor and operating conditions
Record the exact part number, technology, cathode system where relevant, maximum terminal-voltage waveform, ripple current, local temperature and startup conditions.
Establish the voltage references
Obtain the manufacturer’s rated voltage, category-voltage table and recommended application curves. Record the reference used by each percentage and the temperature range where it applies.
Combine the requirements correctly
Use the lowest independent allowable voltage. Multiply ratios only when the manufacturer applies an application margin to category voltage. Check the maximum terminal waveform against the resulting limit.
Check heating, surge exposure and usable capacitance
Assess ripple losses, capacitor temperature, source impedance and startup transients. Verify effective capacitance and use the applicable manufacturer reliability or lifetime guidance.
Validate and document the selection
Measure relevant voltage and temperature extremes in the equipment. Confirm assembly, qualification and safety requirements. Retain the supporting documents and approve alternatives against the same application limits.

References

The following manufacturer documents support the technology-specific guidance and examples. Product-specific datasheets and agreed specifications take precedence over general guidance.

Jon Rhan, Vishay, Derating Tantalum Capacitors Depends On The Cathode System, Vishay, document 40292, revision 19 July 2024.
Ilia Litvachuck, Vishay, Solid Tantalum Capacitors (With MnO₂ Electrolyte) Voltage Derating, Vishay, document 40246, revision 7 September 2022.
Vishay Sprague, TM3 Solid Tantalum Surface Mount Chip Capacitors and Appended Application and Typical Performance Guidance, Vishay, TM3 revision 2020; appended COTS performance guidance, document 40209, revision 19 September 2022.
Nippon Chemi-Con Corporation, Lifetime of Aluminum Electrolytic Capacitors, Nippon Chemi-Con, undated online technical guidance.
Murata Manufacturing Co., Ltd., Does the Capacitance Change When a DC Voltage Is Applied to Ceramic Capacitors?, Murata, undated Capacitors FAQ.
Murata Manufacturing Co., Ltd., Why Does Acoustic Noise Occur in Ceramic Capacitors, and Does This Have Any Effect on Reliability?, Murata, undated Capacitors FAQ.

Latest technical review and revision: 27 October 2026. Updated category-voltage interpretation, combined derating, worked examples, thermal and reliability guidance, and design-selection checks.