BF256B Equivalent & Substitute Parts

Part Overview

The BF256B is an N-Channel JFET RF transistor manufactured by onsemi, housed in a TO-92-3 through-hole package. This device is rated for 30V operation and carries a maximum drain current of 13mA. The BF256B maintains Active product status and is fully RoHS3 compliant with unlimited moisture sensitivity rating (MSL 1). Substitute parts are identified when equivalent electrical performance is required in applications where package form factor or mounting technology can be adapted to system requirements.

Substiute Parts

BF256B

onsemiIn Stock: 39931BF256B Datasheet

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MMBF4391LT1G

onsemiIn Stock: 54550MMBF4391LT1G Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the BF256B is based on the following critical electrical and mechanical parameters:

Electrical Compatibility Criteria:

• N-Channel JFET configuration
• Voltage rating of 30V or greater (Drain to Source Voltage / Breakdown Voltage)
• Current handling capability sufficient for application requirements

Mechanical Compatibility Criteria:

• Package form factor compatibility with circuit board layout and assembly process
• Mounting technology (through-hole versus surface mount) determines board integration method

The MMBF4391LT1G qualifies as a substitute based on matching N-Channel JFET technology, 30V voltage rating, and superior current handling (50mA drain current at rated conditions). The primary difference is packaging: MMBF4391LT1G uses SOT-23-3 surface-mount technology versus BF256B's TO-92-3 through-hole configuration. This substitution is valid when the application circuit board supports surface-mount assembly or when through-hole to surface-mount adapter solutions are implemented.

Parameter Comparison

Engineering Selection Recommendations

BF256B Selection Criteria:

• Through-hole PCB assembly required
• Legacy circuit board designs with TO-92-3 footprints
• Applications requiring direct pin compatibility with existing layouts

MMBF4391LT1G Selection Criteria:

• Surface-mount PCB assembly capability
• New designs prioritizing compact board space
• Applications where higher current handling (50mA versus 13mA) provides design margin
• Both devices maintain Active product status and ROHS3 compliance, ensuring long-term supply availability and regulatory conformance

Both parts are manufactured by onsemi and carry identical RoHS3 and REACH compliance status. Selection between these devices is determined by mounting technology requirements and circuit board assembly process capabilities rather than electrical performance limitations.

Frequently Asked Questions (FAQ)

Q: Can MMBF4391LT1G directly replace BF256B in an existing circuit?

A: Direct replacement requires PCB layout modification. MMBF4391LT1G uses SOT-23-3 surface-mount packaging while BF256B uses TO-92-3 through-hole packaging. Pin configurations differ in physical layout. Adapter solutions or PCB redesign are necessary for substitution.

Q: What are the key electrical differences between these parts?

A: Both devices are N-Channel JFETs with 30V voltage ratings. The primary electrical difference is maximum drain current: BF256B is rated at 13mA while MMBF4391LT1G is rated at 50mA. MMBF4391LT1G also specifies maximum power dissipation of 225mW. These differences indicate MMBF4391LT1G is suitable for higher-current applications.

Q: Are both parts suitable for RF applications?

A: BF256B is specifically designated as an RF MOSFET JFET in its product description. MMBF4391LT1G is classified as a general-purpose N-Channel JFET. RF suitability depends on specific frequency requirements and impedance matching characteristics not provided in the available parameters.

Q: Do both parts have identical compliance certifications?

A: Yes. Both BF256B and MMBF4391LT1G are ROHS3 compliant, REACH unaffected, and carry MSL 1 (unlimited moisture sensitivity) ratings. Both maintain Active product status with onsemi as manufacturer.

Q: Which part should be selected for new designs?

A: MMBF4391LT1G is recommended for new designs due to surface-mount packaging alignment with modern PCB assembly processes, higher current rating providing design margin, and equivalent compliance certifications. BF256B selection is appropriate only when through-hole assembly is a system requirement.