Primary Capacitor: Temperature Range -40°C to +105°C

Component Specifications

Definition

A primary capacitor is a critical passive electronic component in AC-DC converter circuits that stores electrical energy in an electric field, primarily used for smoothing rectified AC voltage, filtering high-frequency noise, and providing temporary power during load transients. It functions as the main energy reservoir between the rectifier stage and the regulator/load, ensuring stable DC output by reducing ripple voltage and improving power quality.

Working Principle

Operates on electrostatic energy storage principles where charge accumulates on conductive plates separated by a dielectric material. In AC-DC converters, it charges during AC voltage peaks and discharges during troughs, maintaining a more constant DC voltage. The capacitor's reactance decreases with frequency, effectively shunting high-frequency AC components to ground while allowing DC to pass.

Materials

Typically constructed with aluminum electrolytic materials (aluminum foil electrodes, electrolyte, paper separator) for high capacitance values (100μF-10000μF) and voltage ratings (200V-600V). Alternative materials include film capacitors (polypropylene/polyester) for high-frequency applications or ceramic capacitors for small-signal filtering.

Technical Parameters

Parameter	Typical range	Notes & selection driver
ESR	10mΩ-100mΩ
Lifetime	2000-10000 hours at rated temperature
Capacitance	100μF-4700μF
Ripple Current	1A-20A RMS
Voltage Rating	200V-600V DC
Temperature Range	-40°C to +105°C

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

IEC 60384, MIL-PRF-39018, JIS C 5101

Parent Products

This component is used in the following industrial products

AC-DC Converter

An electronic device that converts alternating current (AC) to direct current (DC).

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Engineering Analysis

Risks & Mitigation

Overheating from high ripple current
Voltage overstress causing dielectric breakdown
Electrolyte leakage contaminating circuits
Reduced lifespan at high temperatures
Inrush current surges during startup

FMEA Triads

Trigger: High operating temperature exceeding rated limits
Failure: Electrolyte evaporation leading to capacitance loss and increased ESR
Mitigation: Implement thermal management (heatsinks, ventilation), derate voltage/temperature specifications, use high-temperature rated capacitors

Trigger: Voltage spikes from switching transients or lightning surges
Failure: Dielectric breakdown causing short circuit or catastrophic failure
Mitigation: Add surge protection devices (MOVs, TVS diodes), use capacitors with higher voltage ratings, implement snubber circuits

Trigger: Excessive ripple current beyond component rating
Failure: Internal heating leading to thermal runaway and premature failure
Mitigation: Parallel multiple capacitors to share current, select capacitors with higher ripple current ratings, improve circuit design to reduce ripple

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Capacitance: ±20% typical for electrolytic, ±10% for film; ESR: +50%/-30% of rated value

Test Method

IEC 60384-1 for electrical parameters, MIL-STD-202 for environmental testing, IPC-A-610 for soldering and mounting inspection

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

Check the legal entity, factory address, ownership, certifications, and direct contacts.

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Manufacturers of Primary Capacitor

Manufacturer profiles associated with Primary Capacitor.

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review

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Frequently Asked Questions

What is the main function of a primary capacitor in AC-DC converters?

The primary capacitor stores electrical energy to smooth the rectified AC voltage, reduce ripple, filter high-frequency noise, and provide temporary power during load changes, ensuring stable DC output.

How do I select the right primary capacitor for my AC-DC converter?

Consider capacitance value (based on load current and ripple requirements), voltage rating (at least 1.5 times peak input voltage), ESR (for efficiency and heating), ripple current rating, temperature range, and physical size constraints.

What are common failure modes of primary capacitors?

Electrolyte drying (reduced capacitance), increased ESR (overheating), dielectric breakdown (short circuit), venting/leakage from overpressure, and lead corrosion from environmental factors.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Primary Capacitor