4N25FM Equivalent & Substitute Parts

Part Overview

The 4N25FM is an optoisolator transistor with base output manufactured by onsemi, designed for high-voltage isolation applications requiring 7500Vpk isolation rating. This component integrates an LED input stage with a transistor output stage in a 6-SMD surface mount package. The 4N25FM is classified as obsolete, necessitating identification of active equivalent and substitute parts for new designs and ongoing production requirements. Substitute parts must maintain functional compatibility across isolation voltage, current transfer ratio, output characteristics, and thermal operating range.

Substiute Parts

4N25FM

onsemiIn Stock: 7164N25FM Datasheet

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4N25SM

onsemiIn Stock: 30804N25SM Datasheet

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4N25

Texas InstrumentsIn Stock: 384244N25 Datasheet

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4N25

Texas InstrumentsIn Stock: 384244N25 Datasheet

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4N25-060E

Broadcom LimitedIn Stock: 9864N25-060E Datasheet

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4N25-X001

Vishay Semiconductor Opto DivisionIn Stock: 9924N25-X001 Datasheet

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4N25V

Vishay Semiconductor Opto DivisionIn Stock: 19164N25V Datasheet

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4N25X

Isocom Components 2004 LTDIn Stock: 12014N25X Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the 4N25FM is determined by the following critical parameters:

Mandatory Compatibility Criteria:

• Single channel optoisolator with transistor output and base connection
• DC input type
• Isolation voltage rating of 7500Vpk or higher (for direct replacement) or 5000Vrms minimum (for applications with reduced isolation requirements)
• Current transfer ratio minimum of 20% @ 10mA
• Operating temperature range of -55°C to 100°C
• Vce saturation maximum of 500mV or lower
• Maximum forward current of 60 mA or higher

Package Considerations: The 4N25FM uses 6-SMD surface mount packaging. Substitutes may employ 6-DIP through-hole packaging, which requires PCB redesign and assembly process changes. Surface mount alternatives are preferred for direct board-level replacement without layout modification.

Substitute Parts Identified:

1. 4N25SM (onsemi) – Active surface mount alternative with reduced isolation voltage (4170Vrms)
2. 4N25 (Texas Instruments) – Active through-hole alternative with 5000Vrms isolation
3. 4N25-060E (Broadcom Limited) – Active through-hole alternative with 2500Vrms isolation
4. 4N25-X001 (Vishay Semiconductor Opto Division) – Active through-hole alternative with 5000Vrms isolation
5. 4N25V (Vishay Semiconductor Opto Division) – Active through-hole alternative with 5000Vrms isolation
6. 4N25X (Isocom Components 2004 LTD) – Active through-hole alternative with 5300Vrms isolation

Parameter Comparison

Engineering Selection Recommendations

For Direct Surface Mount Replacement (No PCB Redesign):

The 4N25SM (onsemi) is the only active substitute maintaining the 6-SMD surface mount package format. This part is ROHS3 compliant and REACH unaffected. The isolation voltage is reduced to 4170Vrms compared to the 4N25FM's 7500Vpk specification. Selection of 4N25SM is appropriate only for applications where the reduced isolation voltage meets system requirements.

For Through-Hole Package Substitution (PCB Redesign Required):

Multiple active alternatives exist in 6-DIP through-hole packaging. Selection depends on isolation voltage requirements and compliance certifications:

• 4N25-X001 (Vishay) and 4N25 (Texas Instruments) provide 5000Vrms isolation with ROHS3 compliance (Vishay) or RoHS non-compliance (TI). Both support 50mA output current and 70V maximum output voltage.

• 4N25V (Vishay) offers 5000Vrms isolation with improved Vce saturation (300mV maximum) and ROHS3 compliance, but exhibits slower switching times (11µs turn-on, 7µs turn-off).

• 4N25X (Isocom) provides 5300Vrms isolation with ROHS3 compliance and 2µs switching times matching the original 4N25FM specification.

• 4N25-060E (Broadcom) offers the lowest isolation voltage (2500Vrms) but highest output current capability (100mA) and ROHS3 compliance. This part is suitable only for applications with reduced isolation requirements.

Compliance Considerations:

For new designs requiring RoHS and REACH compliance, select from ROHS3-compliant alternatives: 4N25SM, 4N25-X001, 4N25V, 4N25X, or 4N25-060E. The Texas Instruments 4N25 is RoHS non-compliant and REACH affected, limiting its use in regulated applications.

Frequently Asked Questions (FAQ)

Q: Can the 4N25SM directly replace the 4N25FM without PCB modification?

A: Yes, the 4N25SM maintains identical 6-SMD surface mount packaging and pinout compatibility. However, the isolation voltage is reduced from 7500Vpk to 4170Vrms. Substitution is valid only if your application's isolation voltage requirement does not exceed 4170Vrms.

Q: What is the primary difference between the 4N25FM and through-hole alternatives?

A: The 4N25FM uses 6-SMD surface mount packaging, while alternatives such as 4N25, 4N25-X001, 4N25V, and 4N25X use 6-DIP through-hole packaging. Through-hole substitution requires PCB redesign and assembly process changes. Pin configuration and electrical function remain compatible across all variants.

Q: Which substitute part most closely matches the 4N25FM's isolation voltage specification?

A: The 4N25X (Isocom) provides 5300Vrms isolation, the closest match to the 4N25FM's 7500Vpk specification among active alternatives. However, no active substitute achieves the original 7500Vpk isolation rating. Applications requiring isolation voltage exceeding 5300Vrms may require alternative component families.

Q: Are all substitute parts RoHS compliant?

A: Most active substitutes are ROHS3 compliant: 4N25SM, 4N25-X001, 4N25V, 4N25X, and 4N25-060E. The Texas Instruments 4N25 is RoHS non-compliant. Verify compliance requirements for your application before selection.

Q: What is the significance of the Current Transfer Ratio (CTR) specification?

A: The Current Transfer Ratio of 20% @ 10mA is maintained across all substitute parts. This parameter defines the ratio of output collector current to input LED current and determines the optoisolator's gain. All listed substitutes meet or exceed this minimum specification.

Q: Can the 4N25-060E replace the 4N25FM in high-isolation applications?

A: No. The 4N25-060E provides only 2500Vrms isolation, significantly lower than the 4N25FM's 7500Vpk specification. This part is suitable only for applications with reduced isolation voltage requirements. Verify your system's isolation voltage specification before selecting this substitute.

Q: What output voltage differences exist among substitute parts?

A: The 4N25FM and most substitutes support 30V maximum output voltage. Exceptions include the Texas Instruments 4N25 and 4N25-X001, which support 70V maximum output voltage, and the 4N25V, which supports 32V maximum output voltage. Higher output voltage capability provides design flexibility for applications requiring higher collector-emitter voltage operation.

Q: How do switching times compare across substitute parts?

A: The 4N25FM specifies 2µs turn-on and turn-off times. The 4N25SM, 4N25-X001, and 4N25X maintain this 2µs specification. The 4N25V exhibits slower switching (11µs turn-on, 7µs turn-off), while the 4N25-060E specifies 3µs rise and fall times. Switching speed affects circuit response time in high-frequency applications.