4N28 Optoisolator Equivalent & Substitute Parts

Part Overview

The 4N28 is a single-channel optoisolator transistor with base output manufactured by onsemi, rated for 5300Vrms isolation voltage. This component is classified as obsolete, making identification of equivalent and substitute parts essential for ongoing design support and procurement planning. The 4N28 operates as a DC-input optoisolator with transistor output, suitable for applications requiring galvanic isolation in industrial and consumer electronics.

Substiute Parts

4N28

onsemiIn Stock: 251854N28 Datasheet

Current PartRFQ

4N28M

onsemiIn Stock: 223154N28M Datasheet

DirectRFQ

4N25-000E

Broadcom LimitedIn Stock: 30614N25-000E Datasheet

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4N28

onsemiIn Stock: 251854N28 Datasheet

SimilarRFQ

4N28

onsemiIn Stock: 251854N28 Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the 4N28 optoisolator is determined by the following critical parameters:

Mechanical Compatibility: Package type (6-DIP), pin count, and through-hole mounting must remain consistent to ensure direct board-level replacement without layout modifications.

Electrical Compatibility: Number of channels (1), output type (transistor with base), input type (DC), and maximum output voltage (30V) must match to maintain circuit functionality.

Isolation Performance: Voltage isolation rating determines the maximum voltage differential the optoisolator can withstand. Substitutes with equal or higher isolation voltage are acceptable; lower isolation ratings are not suitable.

Switching Characteristics: Turn-on and turn-off times, along with rise and fall times, affect circuit timing. Substitutes must meet or exceed the speed requirements of the original design.

Current Handling: Forward current (If) and output current capacity must support the application's load requirements.

Temperature Range: Operating temperature limits must encompass the application's thermal environment.

Compliance & Status: Active product status and RoHS compliance are preferred for new designs and long-term availability.

Parameter Comparison

Engineering Selection Recommendations

4N28M (Direct Substitute - onsemi): This part is the active-status equivalent from the same manufacturer. It maintains identical package, channel count, output type, and switching characteristics. The isolation voltage is reduced from 5300Vrms to 4170Vrms, and the maximum forward current is reduced from 100 mA to 60 mA. The operating temperature range is narrower (-40°C to 100°C versus -55°C to 100°C). The 4N28M is ROHS3 compliant and actively manufactured, providing superior long-term availability and supply chain stability compared to the obsolete 4N28.

4N25-000E (Similar Substitute - Broadcom Limited): This part shares the same 6-DIP package and single-channel transistor-output architecture. The isolation voltage is significantly lower at 2500Vrms, representing a 53% reduction from the 4N28 specification. The current transfer ratio is higher at 20% minimum, and the maximum output current is 100 mA. Rise and fall times are specified at 3µs each, compared to the 4N28's 2µs turn-on and turn-off times. The 4N25-000E maintains the full -55°C to 100°C operating range and is ROHS3 compliant. This substitute is suitable only for applications where the lower isolation voltage is acceptable.

Frequently Asked Questions (FAQ)

Q: Can the 4N28M directly replace the 4N28 in all applications?

A: The 4N28M is mechanically and functionally compatible with the 4N28 in terms of package, pinout, and output characteristics. However, the reduced isolation voltage (4170Vrms versus 5300Vrms) and maximum forward current (60 mA versus 100 mA) must be verified against your circuit requirements. The narrower operating temperature range (-40°C to 100°C) may also be a constraint in extreme-temperature environments.

Q: Is the 4N25-000E suitable as a substitute for the 4N28?

A: The 4N25-000E is mechanically compatible and shares the same 6-DIP package and single-channel transistor output. However, the isolation voltage is substantially lower at 2500Vrms. This substitute is only appropriate for applications where the lower isolation specification is acceptable. The faster rise and fall times (3µs) may also require circuit timing verification.

Q: Why is the 4N28 listed as obsolete?

A: The 4N28 is classified as obsolete by onsemi. The 4N28M is the active replacement part from the same manufacturer and should be considered for new designs and ongoing procurement.

Q: Are all three parts pin-compatible?

A: Yes. The 4N28, 4N28M, and 4N25-000E all use the 6-DIP (0.300", 7.62mm) package with identical pinout, enabling direct board-level substitution without layout changes.

Q: What are the key differences in electrical performance between these parts?

A: The primary differences are isolation voltage (4N28: 5300Vrms, 4N28M: 4170Vrms, 4N25-000E: 2500Vrms), maximum forward current (4N28: 100 mA, 4N28M: 60 mA, 4N25-000E: 80 mA), and switching speed (4N28 and 4N28M: 2µs, 4N25-000E: 3µs rise/fall time). Current transfer ratio also varies, with the 4N25-000E offering 20% minimum versus 10% for the onsemi parts.

Q: Which substitute offers the best long-term availability?

A: Both the 4N28M and 4N25-000E are active products with ROHS3 compliance, ensuring better long-term availability than the obsolete 4N28. The 4N28M, being from the original manufacturer onsemi, is the preferred choice for direct replacement in existing designs.