4N31SD Optoisolator Equivalent & Substitute Parts

Part Overview

The 4N31SD is an optoisolator with Darlington output manufactured by onsemi, featuring 5300Vrms isolation voltage and single-channel configuration in 6-SMD surface mount packaging. This component is classified as obsolete, making identification of suitable substitute parts essential for ongoing design support and production continuity. The 4N31SD provides galvanic isolation with Darlington output stage, base connection, and 150mA output current capability, serving applications requiring high-voltage isolation with moderate current switching requirements.

Substiute Parts

4N31SD

onsemiIn Stock: 52624N31SD Datasheet

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4N30SR2M

onsemiIn Stock: 28244N30SR2M Datasheet

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4N31SM

Isocom Components 2004 LTDIn Stock: 52114N31SM Datasheet

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4N31SMT&R

Isocom Components 2004 LTDIn Stock: 11274N31SMT&R Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the 4N31SD is determined by the following critical parameters: single-channel configuration, Darlington output with base connection, 6-SMD surface mount package with gull wing leads, DC input type, and operating temperature range compatibility. The isolation voltage, current transfer ratio, output current capability, and saturation voltage are primary electrical characteristics that define functional equivalence.

Two distinct substitution categories exist:

Category A - Direct Electrical Substitutes (onsemi 4N30SR2M): Maintains identical package, mounting type, output stage configuration, and output current rating. Isolation voltage is reduced to 4170Vrms, current transfer ratio increases to 100% @ 10mA, and Vce saturation improves to 1V. Operating temperature range narrows to -40°C ~ 100°C. Product status is active with RoHS3 compliance.

Category B - Alternative Source Substitutes (Isocom 4N31SM / 4N31SMT&R): Maintains identical package, mounting type, output stage configuration, and operating temperature range. Isolation voltage specification differs (7.5Vpk), output current reduces to 5mA, and current transfer ratio data is not provided. Packaging differs between tube (4N31SM) and tape & reel (4N31SMT&R). Both products are active with RoHS3 compliance.

Parameter Comparison

Engineering Selection Recommendations

4N30SR2M (onsemi): This substitute maintains active product status and RoHS3 compliance, providing continuity with the original manufacturer ecosystem. The reduced isolation voltage (4170Vrms versus 5300Vrms) and narrower operating temperature range (-40°C ~ 100°C versus -55°C ~ 100°C) require circuit-level evaluation. The improved current transfer ratio (100% @ 10mA) and lower Vce saturation (1V) represent enhanced electrical performance. This option is suitable for applications where the lower isolation voltage specification is acceptable and the minimum operating temperature requirement does not fall below -40°C.

4N31SM / 4N31SMT&R (Isocom Components 2004 LTD): These substitutes maintain active product status, RoHS3 compliance, and the full operating temperature range (-55°C ~ 100°C). The critical limitation is reduced output current (5mA versus 150mA), which restricts application scope to low-current switching scenarios. The isolation voltage specification (7.5Vpk) differs in measurement units from the main part, requiring technical clarification for voltage equivalence assessment. Packaging options include tube (4N31SM) and tape & reel (4N31SMT&R) formats. These options are suitable only for applications with output current requirements not exceeding 5mA.

Frequently Asked Questions (FAQ)

Q: Can 4N30SR2M directly replace 4N31SD in all applications?

A: Direct replacement requires verification of two parameters: isolation voltage requirement and minimum operating temperature. The 4N30SR2M provides 4170Vrms isolation (versus 5300Vrms) and operates to -40°C minimum (versus -55°C). If your circuit requires 5300Vrms isolation or operates below -40°C, this substitute is not suitable. If both parameters are within acceptable margins, the improved current transfer ratio and lower saturation voltage represent performance enhancements.

Q: Why do the Isocom substitutes (4N31SM / 4N31SMT&R) have significantly lower output current?

A: The Isocom parts specify 5mA maximum output current per channel, compared to 150mA for the 4N31SD. This represents a fundamental design difference in the output stage and is not a parameter variation. These substitutes are only applicable to circuits designed for low-current switching applications.

Q: What is the difference between 4N31SM and 4N31SMT&R?

A: Both parts are electrically identical. The difference is packaging format: 4N31SM is supplied in tube packaging, while 4N31SMT&R is supplied in tape & reel (TR) format. Selection depends on production volume and assembly equipment compatibility. Tape & reel packaging is standard for high-volume automated assembly; tube packaging is typical for lower volumes or manual assembly.

Q: Are all substitutes RoHS3 compliant?

A: Yes. The 4N30SR2M, 4N31SM, and 4N31SMT&R are all explicitly marked as ROHS3 Compliant. The original 4N31SD does not specify RoHS status. All substitutes meet current environmental compliance requirements.

Q: What does the isolation voltage specification mean, and why does it differ between parts?

A: Isolation voltage specifies the maximum voltage differential that can be safely applied between input and output circuits without electrical breakdown. The 4N31SD specifies 5300Vrms (root mean square AC voltage), while the Isocom parts specify 7.5Vpk (peak voltage). These use different measurement standards and cannot be directly compared numerically. Technical datasheets must be consulted to establish functional equivalence.

Q: Can I use 4N30SR2M in a circuit designed for -55°C operation?

A: No. The 4N30SR2M minimum operating temperature is -40°C. Circuits requiring operation below -40°C must use either the original 4N31SD (if available) or the Isocom alternatives (4N31SM / 4N31SMT&R), which support -55°C minimum temperature.