BF256C Equivalent & Substitute Parts

Part Overview

The BF256C is an RF MOSFET JFET transistor manufactured by onsemi, housed in a TO-92-3 through-hole package. This device is classified as obsolete, with 882 pieces currently available in stock. The BF256C operates at a rated voltage of 30V with a maximum current rating of 18mA, designed for RF applications requiring N-channel JFET configuration.

Due to its obsolete product status, identifying equivalent and substitute parts is necessary for ongoing design support, maintenance, and new production requirements. Active alternatives with comparable electrical characteristics and functional performance are available from the same manufacturer.

Substiute Parts

BF256C

onsemiIn Stock: 898BF256C Datasheet

Current PartRFQ

MMBF5485

onsemiIn Stock: 65234MMBF5485 Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the BF256C is determined by the following critical parameters:

Technology Match: Both the main part and substitute must utilize JFET technology for RF applications.

Configuration Match: N-channel configuration is required to maintain circuit functionality and biasing compatibility.

Voltage Rating Compatibility: The substitute part must have a rated voltage equal to or greater than the BF256C's 30V specification to ensure safe operation within the original circuit design envelope.

Current Rating Compatibility: The substitute must support the required current levels for the application. The BF256C operates at 18mA maximum; substitutes with equal or greater current ratings maintain functional equivalence.

Mounting Type Consideration: The BF256C uses through-hole mounting (TO-92-3 package). Substitutes may employ surface-mount technology (SOT-23-3), requiring PCB redesign and assembly process modifications.

Manufacturer Consistency: onsemi manufactures both the main part and identified substitutes, ensuring design continuity and supply chain reliability.

The MMBF5485 is identified as a functional substitute based on shared JFET N-channel technology and onsemi manufacturing. However, electrical parameter differences exist and must be evaluated for specific application requirements.

Parameter Comparison

Engineering Selection Recommendations

Product Status Consideration: The BF256C is classified as obsolete, while the MMBF5485 maintains active product status with onsemi. Active status ensures continued availability, technical support, and manufacturing consistency for new production requirements.

Compliance and Certifications: Both parts maintain identical REACH Unaffected status and MSL 1 (Unlimited) moisture sensitivity ratings, indicating equivalent environmental compliance and handling requirements.

Voltage Rating Differential: The MMBF5485 is rated at 25V, which is lower than the BF256C's 30V specification. Applications operating near the upper voltage limit of the BF256C may require circuit redesign or alternative part selection to maintain adequate safety margins.

Current Rating Differential: The MMBF5485 supports 10mA maximum current, compared to the BF256C's 18mA rating. High-current RF applications may require verification of circuit current demands before substitution.

Packaging and Assembly Impact: Substitution from TO-92-3 through-hole to SOT-23-3 surface-mount requires PCB layout modification, assembly process changes, and potential rework of existing designs. This substitution is suitable for new designs or complete board redesigns only.

RoHS Compliance: The MMBF5485 is RoHS3 compliant, providing enhanced environmental and regulatory alignment for modern manufacturing and end-of-life requirements.

Frequently Asked Questions (FAQ)

Q: Can the MMBF5485 directly replace the BF256C in existing through-hole PCB designs?

A: No. The MMBF5485 uses SOT-23-3 surface-mount packaging, while the BF256C uses TO-92-3 through-hole packaging. Direct PCB substitution is not possible without board redesign and assembly process modification.

Q: What is the voltage rating impact of substituting the MMBF5485 for the BF256C?

A: The MMBF5485 is rated at 25V, compared to the BF256C's 30V rating. Applications requiring operation at or near 30V must be re-evaluated to ensure the 25V rating provides adequate safety margin for the specific circuit design.

Q: Are there current rating limitations when using the MMBF5485 as a substitute?

A: Yes. The MMBF5485 supports a maximum current of 10mA, while the BF256C supports 18mA. Applications requiring current levels between 10mA and 18mA must be redesigned or alternative parts must be selected.

Q: Do both parts share the same environmental compliance status?

A: Yes. Both the BF256C and MMBF5485 maintain REACH Unaffected status and MSL 1 (Unlimited) moisture sensitivity ratings. The MMBF5485 additionally provides RoHS3 compliance.

Q: Why is the BF256C classified as obsolete?

A: The BF256C is an older RF JFET design. onsemi has transitioned to active production of newer alternatives such as the MMBF5485, which offers improved specifications and modern packaging options.

Q: What are the key electrical parameters that determine substitution compatibility?

A: Substitution compatibility is determined by technology type (JFET), channel configuration (N-channel), voltage rating (equal to or greater than 30V), and current rating (equal to or greater than 18mA). Package type and mounting method are secondary considerations dependent on design flexibility.

Q: Is the MMBF5485 suitable for new RF circuit designs?

A: Yes. The MMBF5485 is an active product with specified RF performance characteristics, including 400MHz frequency capability and 4dB noise figure. It is suitable for new RF designs within its electrical parameter specifications.