TC78 Aluminum Electrolytic Capacitor - Equivalent & Substitute Parts

Part Overview

The TC78 is a 40 µF, 450 V aluminum electrolytic capacitor in axial configuration manufactured by Cornell Dubilier Electronics (CDE). This component is classified as obsolete and is no longer in active production. The TC78 series was designed for general-purpose applications requiring high voltage rating and moderate capacitance values in through-hole mounting format.

Due to its obsolete status, sourcing original TC78 units may present supply chain challenges. Equivalent substitute parts with compatible electrical and mechanical characteristics are available to maintain circuit functionality in legacy equipment or new designs requiring similar performance parameters.

Substiute Parts

TC78

Cornell Dubilier Electronics (CDE)In Stock: 1111TC78 Datasheet

Current PartRFQ

WBR40-350A

Cornell Dubilier Electronics (CDE)In Stock: 1258WBR40-350A Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the TC78 is determined by the following critical parameters:

Primary Compatibility Criteria:

• Capacitance value: 40 µF (exact match required)
• Voltage rating: Minimum 450 V (equal or higher acceptable)
• Package configuration: Axial, Can, Through Hole mounting
• Polarization: Polar (electrolytic type)
• Operating temperature range: -40°C to 85°C minimum

Secondary Compatibility Criteria:

• ESR characteristics at operating frequencies
• Ripple current handling capability
• Physical dimensions (lead spacing and can diameter/length)
• Tolerance specification

The WBR40-350A is identified as a substitute part. However, this part operates at a reduced voltage rating of 350 V compared to the TC78's 450 V specification. Substitution is valid only in applications where the actual operating voltage does not exceed 350 V, providing a safety margin below the component's rated voltage.

Parameter Comparison

Engineering Selection Recommendations

TC78 Selection Criteria: The TC78 is appropriate for applications requiring the full 450 V voltage rating. This component should be selected when circuit design specifies 450 V operation or when safety margins demand the higher voltage rating. The TC78 provides superior ripple current handling at both low and high frequencies, making it suitable for power supply filtering applications with substantial AC ripple components.

WBR40-350A Selection Criteria: The WBR40-350A serves as a substitute only in applications where the maximum operating voltage does not exceed 350 V. This part offers advantages in extended operational lifetime (2000 hours at 85°C versus 1000 hours) and improved RoHS3 compliance status. However, the reduced ripple current ratings (135 mA @ 120 Hz and 175.5 mA @ 100 kHz) restrict its use to low-ripple applications. The smaller physical dimensions may provide layout advantages in space-constrained designs, provided PCB hole spacing accommodates the reduced lead pitch.

Compliance Considerations: The WBR40-350A achieves ROHS3 compliance, whereas the TC78 is RoHS non-compliant. For new equipment designs subject to RoHS regulations, the WBR40-350A is the preferred choice if voltage and ripple current requirements permit.

Voltage Derating: Substitution of WBR40-350A for TC78 is valid only when the actual circuit operating voltage remains below 350 V. Direct substitution in 450 V circuits is not permissible.

Frequently Asked Questions (FAQ)

Q: Can the WBR40-350A replace the TC78 in all applications?

A: No. The WBR40-350A operates at 350 V maximum, compared to the TC78's 450 V rating. Substitution is valid only in circuits where the actual operating voltage does not exceed 350 V. Applications requiring the full 450 V rating must use the TC78 or an equivalent 450 V component.

Q: What is the impact of the different ripple current ratings?

A: The TC78 handles 653 mA ripple current at 120 Hz and 816.25 mA at 2.4 kHz. The WBR40-350A handles only 135 mA at 120 Hz and 175.5 mA at 100 kHz. In applications with high AC ripple content, the TC78's superior ripple current capability is necessary to prevent premature capacitor failure. The WBR40-350A is suitable only for low-ripple applications.

Q: Are there physical installation differences between these parts?

A: Yes. The TC78 measures 1.000" diameter × 2.125" length (25.40 × 53.98 mm), while the WBR40-350A measures 0.650" diameter × 1.830" length (16.51 × 46.48 mm). The WBR40-350A is physically smaller. Verify that PCB hole spacing and component clearances accommodate the smaller dimensions before substitution.

Q: What is the significance of the tolerance difference?

A: The TC78 specifies -10%, +50% tolerance, while the WBR40-350A specifies -10%, +100%. The WBR40-350A's wider tolerance band means capacitance values may deviate further from the nominal 40 µF specification. In precision filtering applications, this difference may affect circuit performance.

Q: Why does the WBR40-350A have a longer operational lifetime?

A: The WBR40-350A is rated for 2000 hours at 85°C, compared to the TC78's 1000 hours. This extended lifetime reflects improved internal construction and materials in the WBR series. However, both components are classified as obsolete, and actual availability may be limited.

Q: Is the WBR40-350A RoHS compliant?

A: Yes. The WBR40-350A is ROHS3 compliant, whereas the TC78 is RoHS non-compliant. For equipment manufactured under RoHS regulations, the WBR40-350A is the preferred substitute when voltage and ripple current requirements permit.

Q: Can I use a higher voltage-rated capacitor as a substitute?

A: Yes, provided all other parameters are compatible. A capacitor rated above 450 V can replace the TC78 if capacitance, package type, mounting method, and ripple current ratings match or exceed the TC78 specifications. However, the WBR40-350A, rated below 450 V, cannot be used in 450 V applications.

Q: What should I verify before substituting these parts?

A: Verify the following: (1) actual circuit operating voltage does not exceed the substitute part's voltage rating; (2) ripple current in the application does not exceed the substitute part's rating; (3) physical dimensions fit the PCB layout; (4) tolerance specification is acceptable for circuit function; (5) compliance requirements (RoHS, REACH) are met.