BF245B Equivalent & Substitute Parts

Part Overview

The BF245B is an N-Channel JFET RF transistor manufactured by onsemi, housed in a TO-92-3 (TO-226) through-hole package. This device is rated for 30V operation with a maximum drain current of 100mA and is designed for RF applications requiring field-effect transistor performance in a compact through-hole form factor.

The BF245B is classified as obsolete. Locating equivalent or substitute components is necessary for new designs, production continuity, and system maintenance where through-hole or surface-mount alternatives are required.

Substiute Parts

BF245B

onsemiIn Stock: 5276BF245B Datasheet

Current PartRFQ

BF256B

onsemiIn Stock: 39931BF256B Datasheet

DirectRFQ

MMBF5485

onsemiIn Stock: 65234MMBF5485 Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the BF245B is determined by the following critical parameters:

Primary Substitution Criteria:

• Technology: N-Channel JFET
• Voltage Rating: Minimum 30V (equal or greater)
• Current Rating: Minimum 100mA (equal or greater)
• Package Compatibility: Through-hole or surface-mount alternatives acceptable depending on application requirements

Identified Substitute Categories:

Direct Substitute (BF245B → BF256B): The BF256B maintains identical voltage rating (30V), N-Channel JFET technology, and through-hole TO-92-3 packaging. However, the current rating is reduced to 13mA, which represents a significant limitation for applications requiring the full 100mA capability of the original device.

Similar Substitute (BF245B → MMBF5485): The MMBF5485 provides N-Channel JFET technology in an active product status with RoHS3 compliance. This device operates at a lower voltage rating (25V maximum, 15V test voltage) and reduced current rating (10mA), with a surface-mount SOT-23-3 package. The MMBF5485 includes additional RF performance specifications (400MHz frequency, 4dB noise figure) not present in the original BF245B datasheet parameters.

Parameter Comparison

Engineering Selection Recommendations

For Through-Hole Applications with Active Product Status:

The BF256B is the primary substitute for through-hole mounting applications. This device maintains the same package form factor (TO-92-3) and voltage rating (30V) as the BF245B. The BF256B is currently in active production status and meets ROHS3 compliance requirements, making it suitable for new designs and production environments with RoHS mandates. The reduced current rating (13mA versus 100mA) must be evaluated against specific circuit requirements.

For Surface-Mount Applications with Modern Compliance:

The MMBF5485 provides an alternative for designs transitioning to surface-mount technology. This device is active in production and ROHS3 compliant. The voltage rating is reduced to 25V maximum, and current rating is 10mA. The MMBF5485 includes specified RF performance parameters (400MHz frequency response, 4dB noise figure) not documented in the BF245B specifications. Selection of this device requires confirmation that the reduced voltage and current ratings are compatible with the target application.

Compliance Considerations:

Both substitute parts (BF256B and MMBF5485) are ROHS3 compliant and REACH unaffected, addressing regulatory requirements that may not be met by the obsolete, non-compliant BF245B.

Frequently Asked Questions (FAQ)

Q: Can the BF256B directly replace the BF245B in existing through-hole designs?

A: The BF256B shares the same TO-92-3 package and 30V voltage rating as the BF245B, enabling physical and electrical compatibility for voltage specifications. However, the current rating is reduced from 100mA to 13mA. Designs operating at or near the 100mA specification of the original device require circuit re-evaluation.

Q: What is the primary difference between the BF256B and MMBF5485 substitutes?

A: The BF256B maintains through-hole mounting (TO-92-3 package) and 30V voltage rating. The MMBF5485 transitions to surface-mount technology (SOT-23-3 package) with a reduced 25V maximum voltage rating. The MMBF5485 includes documented RF performance specifications (400MHz, 4dB noise figure) not present in the BF245B datasheet.

Q: Are both substitute parts RoHS compliant?

A: Yes. Both the BF256B and MMBF5485 are ROHS3 compliant. The original BF245B is RoHS non-compliant. This compliance difference is significant for applications subject to RoHS regulations.

Q: Can the MMBF5485 be used in applications requiring 30V operation?

A: No. The MMBF5485 has a maximum voltage rating of 25V, which is below the 30V specification of the BF245B. Applications requiring 30V operation must use the BF256B or identify alternative components with appropriate voltage ratings.

Q: What mounting considerations apply when selecting between these substitutes?

A: The BF245B and BF256B both use through-hole TO-92-3 packages suitable for traditional PCB assembly. The MMBF5485 uses a surface-mount SOT-23-3 package, requiring surface-mount assembly equipment and PCB layout modifications. Package selection depends on manufacturing capabilities and PCB design constraints.

Q: How do the current ratings affect device selection?

A: The BF245B is rated for 100mA maximum drain current. The BF256B is rated for 13mA, and the MMBF5485 is rated for 10mA. Applications requiring high current operation must verify that the reduced ratings of substitute devices are compatible with circuit specifications. Lower current ratings may limit RF power output or require circuit redesign.