6N138 Optoisolator Darlington with Base Output

Part Overview

The 6N138 is a single-channel optoisolator with Darlington output and base connection, rated for 2500Vrms isolation voltage. This component is classified as obsolete, making equivalent and substitute parts necessary for new designs and ongoing production support. The 6N138 provides DC input isolation with Darlington output configuration, suitable for applications requiring galvanic isolation in logic and control circuits.

Substiute Parts

6N138

onsemiIn Stock: 121546N138 Datasheet

Current PartRFQ

6N138M

Fairchild SemiconductorIn Stock: 155116N138M Datasheet

DirectRFQ

6N138

Fairchild SemiconductorIn Stock: 121646N138 Datasheet

DirectRFQ

6N138

Fairchild SemiconductorIn Stock: 121646N138 Datasheet

DirectRFQ

6N138-000E

Broadcom LimitedIn Stock: 18296N138-000E Datasheet

SimilarRFQ

6N138-020E

Broadcom LimitedIn Stock: 8506N138-020E Datasheet

SimilarRFQ

HCPL-4701

Broadcom LimitedIn Stock: 1950HCPL-4701 Datasheet

SimilarRFQ

HCPL-4701-000E

Broadcom LimitedIn Stock: 5791HCPL-4701-000E Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution for the 6N138 is determined by the following critical parameters:

• Package compatibility: 8-DIP form factor with 0.300" (7.62mm) body width
• Isolation voltage: Minimum 2500Vrms (higher ratings are acceptable)
• Output configuration: Darlington with Base output
• Number of channels: Single channel
• Current transfer ratio: Minimum 300% @ 1.6mA
• Maximum output current: 60mA per channel
• Input type: DC
• Mounting: Through Hole

Substitute parts are grouped into two categories:

Direct Substitutes maintain identical or superior electrical specifications and package dimensions, allowing pin-for-pin replacement.

Similar Substitutes meet the core functional requirements but may have different isolation voltage ratings, current transfer ratio ranges, or operating temperature ranges. These require circuit validation before implementation.

Parameter Comparison

Engineering Selection Recommendations

For direct pin-for-pin replacement with active product status:

6N138-020E (Broadcom Limited) and 6N138-000E (Broadcom Limited) are the primary substitutes. Both maintain the 8-DIP (0.300", 7.62mm) package, support 300% minimum current transfer ratio at 1.6mA input, and deliver 60mA output current. The 6N138-020E provides 5000Vrms isolation, exceeding the original 2500Vrms specification. Both parts are ROHS3 compliant and carry active product status, ensuring long-term availability.

For applications requiring extended temperature range:

The Fairchild Semiconductor 6N138 (Tube packaging) extends the operating temperature to -55°C ~ 100°C, though this part is obsolete. The 6N138M variant from Fairchild offers active status but uses a wider 8-DIP (0.400", 10.16mm) package, requiring PCB layout verification before implementation.

For applications with higher isolation voltage requirements:

The 6N138-020E and 6N138M both provide 5000Vrms isolation, suitable for applications demanding enhanced galvanic separation.

For applications with different switching speed or output voltage requirements:

HCPL-4701 and HCPL-4701-000E offer higher maximum output voltage (18V) and higher current transfer ratio (600% minimum @ 500µA), but exhibit slower switching times (3µs turn-on, 34µs turn-off) compared to the original 6N138. These parts are suitable only if circuit timing requirements accommodate the extended switching delays. HCPL-4701-000E is ROHS3 compliant; HCPL-4701 is RoHS non-compliant.

Frequently Asked Questions (FAQ)

Q: Can the 6N138M be used as a direct replacement?

A: The 6N138M maintains electrical compatibility but uses an 8-DIP (0.400", 10.16mm) package versus the original 0.300" width. PCB footprint verification is required. Pin configuration remains compatible.

Q: What is the key difference between 6N138-000E and 6N138-020E?

A: Both are Broadcom parts in identical 8-DIP (0.300", 7.62mm) packages with ROHS3 compliance. The 6N138-000E provides 3750Vrms isolation; the 6N138-020E provides 5000Vrms isolation. Selection depends on circuit isolation voltage requirements.

Q: Are HCPL-4701 variants suitable replacements?

A: HCPL-4701 and HCPL-4701-000E meet the package, channel count, and output current specifications. However, they exhibit significantly slower switching times (3µs turn-on versus 1.5µs for the original) and operate within a narrower temperature range (0°C ~ 70°C). Use only if circuit timing permits the extended delays.

Q: Which substitute offers the best compliance profile?

A: 6N138-020E and HCPL-4701-000E both carry ROHS3 compliance and active product status. The 6N138-020E is recommended for standard applications; HCPL-4701-000E is an alternative if higher output voltage (18V) is required.

Q: Can substitutes be mixed in the same design?

A: No. Select a single substitute part for consistency. Mixing different optoisolator types introduces timing and performance variability across the circuit.

Q: What is the impact of higher isolation voltage ratings?

A: Higher isolation voltage (5000Vrms versus 2500Vrms) provides enhanced safety margin and is fully compatible with circuits designed for the original specification. No circuit modification is required.