IL251 Optoisolator Transistor with Base Output - Equivalent & Substitute Parts

Part Overview

The IL251 is an optoisolator transistor with base output manufactured by Vishay Semiconductor Opto Division, rated for 5300Vrms isolation voltage in a 6-DIP through-hole package. This component provides galvanic isolation for AC and DC input signals with transistor output capability. The IL251 is classified as obsolete, making equivalent substitute parts necessary for new designs and ongoing production support. Substitute parts must maintain compatibility across isolation voltage, channel configuration, output type, package form factor, and thermal operating range.

Substiute Parts

IL251

Vishay Semiconductor Opto DivisionIn Stock: 97223IL251 Datasheet

Current PartRFQ

H11AA1

Quality TechnologiesIn Stock: 15777H11AA1 Datasheet

MFR RecommendedRFQ

H11AA1X

Isocom Components 2004 LTDIn Stock: 1857H11AA1X Datasheet

MFR RecommendedRFQ

H11AA2

Fairchild SemiconductorIn Stock: 6959H11AA2 Datasheet

MFR RecommendedRFQ

H11AA3

onsemiIn Stock: 2002H11AA3 Datasheet

MFR RecommendedRFQ

H11AA4

onsemiIn Stock: 8422H11AA4 Datasheet

MFR RecommendedRFQ

H11AA4VM

onsemiIn Stock: 12157H11AA4VM Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the IL251 are grouped based on the following critical parameters that determine functional equivalence:

Primary Compatibility Criteria:

• Single channel optoisolator configuration
• Transistor with base output type
• 6-DIP through-hole package (0.300", 7.62mm)
• AC and DC input capability
• Isolation voltage rating of 5000Vrms or higher
• Maximum output voltage of 30V or greater
• Vce saturation of 400mV or lower
• Operating temperature range encompassing -55°C to 100°C or compatible subset
• ROHS3 compliance

Substitution Logic: Parts are considered equivalent when they maintain the same package footprint, channel count, output topology, and isolation voltage class. Variations in current transfer ratio, forward voltage, and maximum forward current are acceptable provided they do not exceed the specified maximums. Parts with lower isolation voltage ratings (H11AA4VM at 4170Vrms) may be used in applications where the full 5300Vrms isolation is not required. Product status (active vs. obsolete) indicates availability but does not affect electrical compatibility.

Parameter Comparison

Engineering Selection Recommendations

Preferred Active Substitutes:

H11AA4VM and H11AA1X are the recommended primary substitutes for the IL251. Both parts are currently in active production status, ensuring long-term availability and supply chain stability. H11AA4VM offers 4170Vrms isolation (lower than IL251 but suitable for most applications not requiring full 5300Vrms isolation), 100% minimum current transfer ratio, and ROHS3 compliance. H11AA1X maintains the full 5300Vrms isolation rating matching the IL251, with 20% minimum current transfer ratio and ROHS3 compliance.

Secondary Active Substitute:

H11AA1 from Quality Technologies is active and provides equivalent electrical performance with 20% minimum current transfer ratio and ROHS3 compliance. Operating temperature range is -40°C to 100°C, which is narrower than the IL251 but suitable for most industrial applications.

Obsolete Alternatives (Use Only When Active Substitutes Unavailable):

H11AA2, H11AA3, and H11AA4 are obsolete parts but may be available from inventory. H11AA2 provides 5000Vrms isolation with lower 10% minimum current transfer ratio. H11AA3 and H11AA4 maintain 5300Vrms isolation with higher current transfer ratios (50% and 100% respectively) and extended forward current capability (100 mA maximum).

Isolation Voltage Considerations:

Applications requiring the full 5300Vrms isolation rating must use H11AA1X, H11AA3, or H11AA4. Applications tolerating 5000Vrms or 4170Vrms isolation may use H11AA2 or H11AA4VM respectively, which may offer better availability.

Frequently Asked Questions (FAQ)

Q: Can H11AA4VM replace IL251 in all applications?

A: H11AA4VM is suitable for applications where 4170Vrms isolation is sufficient. If your design requires the full 5300Vrms isolation rating of the IL251, use H11AA1X instead. Both parts share identical 6-DIP package footprint and output topology.

Q: What is the difference between H11AA1 and H11AA1X?

A: H11AA1 does not specify isolation voltage rating, while H11AA1X explicitly rates 5300Vrms isolation matching the IL251. Both maintain 20% minimum current transfer ratio and 6-DIP package compatibility. H11AA1X is preferred when isolation voltage specification is critical.

Q: Are all substitute parts ROHS3 compliant?

A: H11AA4VM, H11AA1X, H11AA1, and H11AA2 are confirmed ROHS3 compliant. H11AA3 and H11AA4 do not specify RoHS status in available documentation. Verify RoHS compliance with the manufacturer if regulatory compliance is required.

Q: Can I use H11AA2 as a direct replacement for IL251?

A: H11AA2 is electrically compatible but has lower 10% minimum current transfer ratio compared to IL251's 20%, and 5000Vrms isolation versus 5300Vrms. It is obsolete. Use only if active substitutes are unavailable and your application tolerates the lower current transfer ratio specification.

Q: What is the impact of different current transfer ratios?

A: Current transfer ratio determines the output current for a given input current. IL251 specifies 20% minimum, while H11AA3 and H11AA4 specify 50% and 100% respectively. Higher current transfer ratios provide greater output current capability for the same input drive. Lower ratios require higher input current to achieve the same output current.

Q: Are there any temperature range limitations with substitute parts?

A: IL251 operates -55°C to 100°C. H11AA1 and H11AA4VM operate -40°C to 100°C (narrower low-temperature range). H11AA1X operates -30°C to 100°C. If your application requires operation below -40°C, use H11AA2, H11AA3, or H11AA4 which maintain the full -55°C to 100°C range.

Q: Do all substitute parts use the same 6-DIP package?

A: Yes. All substitute parts listed use 6-DIP (0.300", 7.62mm) through-hole package, ensuring direct pin-compatible replacement on existing PCBs without layout modification.