4N31S Optoisolator Equivalent & Substitute Parts

Part Overview

The 4N31S is an optoisolator with Darlington output and base connection, manufactured by onsemi. This component provides 5300Vrms isolation voltage in a 6-SMD surface mount package. The part is currently obsolete, making equivalent and substitute parts necessary for ongoing system support and new designs requiring similar functionality.

Key Parameters

Parameter	Value
Manufacturer Part Number	4N31S
Manufacturer	onsemi
Category	Optoisolators
Number of Channels	1
Voltage - Isolation	5300Vrms
Current Transfer Ratio (Min)	50% @ 10mA
Output Type	Darlington with Base
Voltage - Output (Max)	30V
Current - Output / Channel	150mA
Turn On / Turn Off Time (Typ)	5µs, 40µs (Max)
Operating Temperature	-55°C ~ 100°C
Mounting Type	Surface Mount
Package / Case	6-SMD, Gull Wing
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution for the 4N31S is determined by the following critical parameters:

Package Type: 6-SMD, Gull Wing surface mount configuration
Output Configuration: Darlington with Base output
Number of Channels: Single channel
Input Type: DC
Isolation Voltage: Minimum 4170Vrms (acceptable reduction from 5300Vrms)
Output Voltage Rating: 30V maximum
Output Current Capability: Minimum 5mA per channel
Switching Speed: Turn on/off times of 5µs and 40µs (Max)
Operating Temperature Range: -55°C to 100°C minimum
Mounting Type: Surface Mount

The substitute parts listed below meet these core electrical and mechanical requirements while maintaining functional compatibility with the 4N31S in typical applications.

Parameter Comparison

Parameter	4N31S (onsemi)	4N30SM (Fairchild)	4N31SM (Isocom)	4N31SMT&R (Isocom)
Voltage - Isolation	5300Vrms	4170Vrms	7.5Vpk	7.5Vpk
Current Transfer Ratio (Min)	50% @ 10mA	100% @ 10mA	Not specified	Not specified
Output Type	Darlington with Base	Darlington with Base	Darlington with Base	Darlington with Base
Voltage - Output (Max)	30V	30V	30V	30V
Current - Output / Channel	150mA	150mA	5mA	5mA
Turn On / Turn Off Time (Typ)	5µs, 40µs (Max)	5µs, 40µs (Max)	5µs, 40µs (Max)	5µs, 40µs (Max)
Vce Saturation (Max)	1.2V	1V	1.2V	1.2V
Operating Temperature	-55°C ~ 100°C	-40°C ~ 100°C	-55°C ~ 100°C	-55°C ~ 100°C
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Package / Case	6-SMD, Gull Wing	6-SMD, Gull Wing	6-SMD, Gull Wing	6-SMD, Gull Wing
Product Status	Obsolete	Active	Active	Active

Engineering Selection Recommendations

4N30SM (Fairchild Semiconductor): This part is active and maintains the same 150mA output current capability as the 4N31S. The isolation voltage is reduced to 4170Vrms, which is acceptable for applications not requiring the full 5300Vrms specification. The current transfer ratio is improved at 100% @ 10mA. Operating temperature range is -40°C to 100°C, which covers most industrial applications but does not extend to -55°C. This part is suitable for designs where the lower isolation voltage is acceptable and the reduced low-temperature rating is not a constraint.

4N31SM (Isocom Components 2004 LTD): This part is active and maintains the full -55°C to 100°C operating temperature range. However, the output current is limited to 5mA per channel, significantly lower than the 4N31S specification of 150mA. This part is suitable only for low-current applications. The part is RoHS3 compliant and REACH unaffected.

4N31SMT&R (Isocom Components 2004 LTD): Functionally identical to 4N31SM but supplied in Tape & Reel packaging instead of Tube. This variant is active, maintains the -55°C to 100°C operating temperature range, and is RoHS3 compliant. The 5mA output current limitation applies. This packaging option is suitable for high-volume automated assembly processes.

Frequently Asked Questions (FAQ)

Q: Can 4N30SM directly replace 4N31S in all applications?

A: The 4N30SM is electrically compatible for most applications due to matching output current (150mA), output voltage (30V), and switching speed specifications. The primary difference is the reduced isolation voltage (4170Vrms vs. 5300Vrms). Applications requiring the full 5300Vrms isolation specification must evaluate whether 4170Vrms meets their safety and regulatory requirements. The operating temperature range is also reduced to -40°C minimum, which may not be suitable for extreme cold environments.

Q: Why do the Isocom parts (4N31SM and 4N31SMT&R) have lower output current?

A: The Isocom variants are specified for 5mA output current per channel, compared to 150mA for the 4N31S and 4N30SM. These parts are suitable only for signal-level isolation applications where output current requirements are minimal. Applications requiring 150mA output current cannot use these substitutes.

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

A: Both parts are functionally identical with the same electrical specifications. The difference is packaging: 4N31SM is supplied in Tube packaging for manual handling and lower-volume applications, while 4N31SMT&R is supplied in Tape & Reel format for automated pick-and-place assembly in high-volume production.

Q: Are all substitute parts RoHS compliant?

A: The 4N30SM compliance status is not specified in the provided data. The Isocom parts (4N31SM and 4N31SMT&R) are RoHS3 compliant. The original 4N31S does not list RoHS status. Verify RoHS compliance requirements with your specific application and regulatory environment.

Q: Can I use 4N31SM as a direct replacement for 4N31S?

A: No. While the 4N31SM maintains the same operating temperature range (-55°C to 100°C) and package type, the output current is limited to 5mA compared to the 4N31S specification of 150mA. This part is suitable only for low-current signal isolation applications and cannot support higher current loads.

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