4N27FM Equivalent & Substitute Parts

Part Overview

The 4N27FM is an optoisolator transistor with base output manufactured by onsemi, designed for high-voltage isolation applications requiring 7500Vpk isolation rating. This component features a single channel with transistor output and base connection in a 6-SMD surface mount package. The part is currently classified as obsolete, making identification of suitable substitute components essential for ongoing design support and production continuity.

Substiute Parts

4N27FM

onsemiIn Stock: 8284N27FM Datasheet

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4N27SM

onsemiIn Stock: 164844N27SM Datasheet

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4N27

Texas InstrumentsIn Stock: 136974N27 Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the 4N27FM is determined by the following critical parameters that must remain compatible:

Mandatory Compatibility Parameters:

• Number of Channels: 1 (single channel requirement)
• Output Type: Transistor with Base (functional output configuration)
• Current Transfer Ratio (Min): 10% @ 10mA (minimum performance threshold)
• Voltage - Forward (Vf) (Typ): 1.18V (input diode forward voltage)
• Current - DC Forward (If) (Max): 60 mA (maximum input current)
• Vce Saturation (Max): 500mV (output saturation voltage)
• Turn On / Turn Off Time (Typ): 2µs, 2µs (switching speed)
• Input Type: DC (input signal type)

Isolation Voltage Consideration: The 4N27FM specifies 7500Vpk isolation. Substitute parts may have different isolation voltage ratings (expressed in Vpk or Vrms) provided they meet or exceed the application requirement. Lower isolation ratings represent a functional downgrade and are not suitable substitutes.

Package Compatibility: The 4N27FM uses 6-SMD surface mount packaging. Substitutes with different package types (such as 6-DIP through-hole) require PCB redesign and are considered cross-functional alternatives rather than direct substitutes.

Parameter Comparison

Engineering Selection Recommendations

4N27SM (onsemi) - Surface Mount Substitute: The 4N27SM is the preferred direct substitute for the 4N27FM when isolation voltage requirements can be met at 4170Vrms. Both parts share identical surface mount packaging (6-SMD, Gull Wing), matching input/output electrical characteristics, and equivalent switching performance. The 4N27SM is currently in active production status with ROHS3 compliance, providing long-term supply availability. The reduced isolation voltage (4170Vrms versus 7500Vpk) represents a functional downgrade and is acceptable only if the application isolation requirement does not exceed 4170Vrms.

4N27 (Texas Instruments) - Cross-Functional Alternative: The Texas Instruments 4N27 provides equivalent electrical performance with higher maximum output voltage (70V versus 30V) and maintains the same current transfer ratio and saturation characteristics. However, this part uses through-hole 6-DIP packaging, requiring PCB redesign and assembly process changes from the original surface mount configuration. The 4N27 is suitable only when PCB layout modifications are feasible. This part is RoHS non-compliant and REACH-affected, which may restrict use in regulated applications.

Frequently Asked Questions (FAQ)

Q: Can the 4N27SM directly replace the 4N27FM without PCB modifications? A: Yes, the 4N27SM is a direct pin-compatible substitute in the same 6-SMD surface mount package. No PCB layout changes are required. However, verify that your application isolation voltage requirement does not exceed 4170Vrms, as this represents a reduction from the 4N27FM specification of 7500Vpk.

Q: What is the difference between Vpk and Vrms isolation voltage ratings? A: Vpk (peak voltage) and Vrms (RMS voltage) are different measurement standards for isolation voltage. The 4N27FM specifies 7500Vpk, while the 4N27SM specifies 4170Vrms. These values are not directly comparable without conversion factors specific to the test waveform. Consult manufacturer datasheets for equivalent isolation performance in your application.

Q: Why is the Texas Instruments 4N27 not recommended as a direct substitute? A: The Texas Instruments 4N27 uses 6-DIP through-hole packaging, while the 4N27FM uses 6-SMD surface mount packaging. This package difference requires PCB redesign and changes to assembly processes. Additionally, the Texas Instruments part is RoHS non-compliant, which may conflict with regulatory requirements in your application.

Q: Is the 4N27SM suitable for applications requiring 7500Vpk isolation? A: No. The 4N27SM isolation rating of 4170Vrms is lower than the 4N27FM specification of 7500Vpk. Use the 4N27SM only when your application isolation requirement is 4170Vrms or lower.

Q: What is the operating temperature range difference between the 4N27FM and 4N27SM? A: The 4N27FM operates from -55°C to 100°C, while the 4N27SM operates from -40°C to 100°C. The 4N27SM has a narrower low-temperature range. Verify that your application does not require operation below -40°C before selecting the 4N27SM.

Q: Are there compliance or supply chain advantages to using the 4N27SM? A: Yes. The 4N27SM is in active production status with ROHS3 compliance and REACH unaffected status, providing better long-term availability and regulatory alignment compared to the obsolete 4N27FM. The 4N27SM also has significantly higher inventory availability (16,400 pcs versus 818 pcs for the 4N27FM).