IL256AT Optoisolator Equivalent & Substitute Parts

Part Overview

The IL256AT is a 4000Vrms optoisolator transistor with base output manufactured by Vishay Semiconductor Opto Division. This component provides galvanic isolation for AC and DC input signals with a single-channel transistor output configuration in an 8-SOIC surface mount package. The IL256AT is currently in Last Time Buy status, making identification of functionally equivalent alternatives necessary for ongoing design support and procurement planning.

Substiute Parts

IL256AT

Vishay Semiconductor Opto DivisionIn Stock: 6743IL256AT Datasheet

Current PartRFQ

MOC256M

Fairchild SemiconductorIn Stock: 13479MOC256M Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the IL256AT is determined by the following critical parameters:

• Isolation Voltage: Minimum 4000Vrms required for equivalent isolation performance
• Output Configuration: Transistor with base output mandatory for circuit compatibility
• Current Transfer Ratio: Minimum 20% @ 10mA to maintain signal transfer characteristics
• Package Type: 8-SOIC surface mount package for PCB compatibility
• Input Type: AC/DC input capability for signal flexibility
• Output Voltage Rating: 30V maximum output voltage
• Saturation Characteristics: Vce saturation at 400mV maximum

The MOC256M from Fairchild Semiconductor meets the core functional requirements of single-channel optoisolation with transistor output in an 8-SOIC package. However, the MOC256M operates at 2500Vrms isolation voltage, which is lower than the IL256AT's 4000Vrms specification. This represents a trade-off in isolation capability and must be evaluated against specific application requirements.

Parameter Comparison

Engineering Selection Recommendations

The IL256AT is designated Last Time Buy status, indicating limited future availability. The MOC256M is an Active product from Fairchild Semiconductor with higher current output capability (150mA vs. unspecified for IL256AT) and greater inventory availability (13,400 pcs vs. 6,720 pcs).

Selection between these components depends on isolation voltage requirements. Applications requiring 4000Vrms isolation must retain the IL256AT or identify alternative sources meeting this specification. Applications tolerating 2500Vrms isolation can transition to the MOC256M, which offers the advantage of active product status and higher output current capacity.

Both components share identical package geometry (8-SOIC), current transfer ratio (20% @ 10mA), input/output voltage characteristics, and saturation behavior, enabling direct PCB footprint compatibility. Operating temperature ranges differ by 15°C at the lower bound (IL256AT: -55°C vs. MOC256M: -40°C), which may be relevant for extended temperature applications.

Frequently Asked Questions (FAQ)

Q: Can MOC256M directly replace IL256AT in all applications?

A: Direct replacement is possible only in applications where 2500Vrms isolation voltage is acceptable. The IL256AT provides 4000Vrms isolation, which is 1500Vrms higher. Applications designed for 4000Vrms isolation require components meeting this specification.

Q: Are the packages physically identical?

A: Yes. Both IL256AT and MOC256M use 8-SOIC packages with 0.154" (3.90mm) width, enabling identical PCB footprints and no layout modifications.

Q: What is the difference in output current capability?

A: The MOC256M specifies 150mA maximum output current per channel. The IL256AT does not specify this parameter in the provided data. Circuits designed around the IL256AT's unspecified output current must be evaluated against the MOC256M's 150mA rating.

Q: How do the input characteristics compare?

A: Both components accept AC and DC input signals with identical forward voltage (1.2V typical) and maximum DC forward current (60mA). Input stage behavior is equivalent.

Q: What is the significance of product status?

A: IL256AT is Last Time Buy, meaning Vishay will discontinue production. MOC256M is Active, indicating ongoing manufacturing and availability. For new designs or long-term procurement, Active status provides supply continuity.

Q: Do operating temperature ranges affect substitution?

A: IL256AT operates from -55°C to 100°C, while MOC256M operates from -40°C to 100°C. Applications requiring operation below -40°C must use IL256AT or identify alternative components with extended low-temperature ratings.

Q: Are compliance certifications equivalent?

A: IL256AT is ROHS3 Compliant with REACH Unaffected status. MOC256M compliance information is not provided in the available data. Compliance verification is required for regulated applications.