4N28FM Optoisolator Equivalent & Substitute Parts

Part Overview

The 4N28FM is an optoisolator transistor with base output manufactured by onsemi, designed for high-voltage isolation applications. This component features a single channel with 7500Vpk isolation rating and transistor output with base connection in a 6-SMD surface mount package. The product is currently obsolete, making identification of equivalent and substitute parts essential for design continuity and procurement planning.

Substiute Parts

4N28FM

onsemiIn Stock: 11754N28FM Datasheet

Current PartRFQ

4N28SM

onsemiIn Stock: 28004N28SM Datasheet

SimilarRFQ

4N28

onsemiIn Stock: 251854N28 Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the 4N28FM is determined by the following critical parameters:

• Number of Channels: Must be 1 channel
• Output Type: Must be Transistor with Base
• Voltage - Isolation: Minimum 7500Vpk (or equivalent Vrms rating)
• Current Transfer Ratio (Min): Minimum 10% @ 10mA
• Voltage - Output (Max): 30V or greater
• Vce Saturation (Max): 500mV or lower
• Turn On / Turn Off Time (Typ): 2µs or faster
• Voltage - Forward (Vf) (Typ): 1.18V
• Current - DC Forward (If) (Max): 60 mA or greater
• Operating Temperature Range: Must encompass -55°C to 100°C or be compatible with application requirements
• Mounting Type: Surface Mount preferred for direct replacement
• Package / Case: 6-SMD, Gull Wing for PCB compatibility

Based on these parameters, the following parts are identified as substitutes:

4N28SM - Active product with reduced isolation voltage (4170Vrms) but maintains all other critical electrical characteristics and surface mount packaging.

4N28 - Obsolete product with different isolation voltage (5300Vrms) and through-hole DIP packaging, suitable only for applications where package type change is acceptable.

Parameter Comparison

Engineering Selection Recommendations

4N28SM is the primary substitute for 4N28FM applications. This part maintains identical surface mount packaging (6-SMD, Gull Wing), matching electrical characteristics for current transfer ratio, output voltage, saturation voltage, and switching times. The 4N28SM is an active product with current manufacturing support and ROHS3 compliance. The isolation voltage is reduced from 7500Vpk to 4170Vrms; selection of this substitute requires confirmation that the application isolation requirement does not exceed 4170Vrms.

4N28 is a secondary substitute suitable only for applications where package type conversion from surface mount to through-hole is feasible. This part is obsolete and features different isolation voltage (5300Vrms) and higher maximum forward current (100 mA). Through-hole mounting requires PCB redesign and is not recommended for direct replacement in existing surface mount designs.

For new designs or procurement of replacement components, 4N28SM is the recommended substitute due to active product status and maintained surface mount packaging compatibility.

Frequently Asked Questions (FAQ)

Q: Can 4N28SM directly replace 4N28FM on the same PCB?

A: Yes, 4N28SM can directly replace 4N28FM without PCB modification. Both parts use identical 6-SMD, Gull Wing surface mount packaging. Electrical characteristics including current transfer ratio, output voltage, saturation voltage, and switching times are identical. The primary difference is isolation voltage rating.

Q: What is the isolation voltage difference between 4N28FM and 4N28SM?

A: 4N28FM provides 7500Vpk isolation, while 4N28SM provides 4170Vrms isolation. These are different measurement standards (peak versus RMS). Selection depends on application isolation requirements. If the application requires isolation exceeding 4170Vrms, 4N28SM is not suitable.

Q: Why is 4N28 listed as a substitute if it uses through-hole packaging?

A: 4N28 is listed as a substitute based on matching electrical characteristics (single channel, transistor with base output, identical current transfer ratio and switching times). However, the through-hole 6-DIP package requires PCB redesign and is not recommended for direct replacement in surface mount applications.

Q: What is the product status significance for component selection?

A: 4N28FM and 4N28 are both obsolete products with limited availability. 4N28SM is an active product with ongoing manufacturing and supply chain support. For new procurement or long-term applications, 4N28SM is the recommended choice due to product status and availability assurance.

Q: Are there compliance differences between these parts?

A: 4N28SM carries ROHS3 compliance certification. 4N28FM and 4N28 do not list RoHS status in available specifications. All three parts are REACH Unaffected and carry EAR99 ECCN classification.

Q: What is the operating temperature range difference?

A: 4N28FM and 4N28 operate from -55°C to 100°C. 4N28SM operates from -40°C to 100°C. If the application requires operation below -40°C, 4N28SM is not suitable; 4N28FM or 4N28 must be used.