BFR31LT1 Equivalent & Substitute Parts

Part Overview

The BFR31LT1 is an N-Channel JFET transistor manufactured by onsemi, housed in a SOT-23-3 (TO-236) surface mount package with a maximum power dissipation of 225 mW. This part is classified as obsolete, making equivalent and substitute parts necessary for new designs and ongoing production requirements. The BFR31LT1 operates across a temperature range of -55°C to 150°C and is rated for a drain-to-source voltage (Vdss) of 25 V with a drain current (Idss) of 1 mA at 10 V.

Key Parameters

Parameter	Value	Unit
Manufacturer Part Number	BFR31LT1	—
Manufacturer	onsemi	—
Category	Transistors (JFET N-Channel)	—
Package / Case	TO-236-3, SC-59, SOT-23-3	—
FET Type	N-Channel	—
Drain to Source Voltage (Vdss)	25	V
Current - Drain (Idss) @ Vds (Vgs=0)	1	mA @ 10 V
Voltage - Cutoff (VGS off) @ Id	2.5	V @ 0.5 nA
Input Capacitance (Ciss) (Max) @ Vds	5	pF @ 10V
Power - Max	225	mW
Operating Temperature	-55 to 150	°C (TJ)
Mounting Type	Surface Mount	—
Product Status	Obsolete	—
RoHS Status	RoHS non-compliant	—

Substitute Part Grouping Explanation

Substitution of the BFR31LT1 is determined by the following critical parameters:

Package Compatibility: All substitute parts must use the SOT-23-3 (TO-236) surface mount package to ensure mechanical and electrical compatibility with existing PCB layouts.
FET Configuration: All substitutes must be N-Channel JFETs to maintain circuit functionality.
Voltage Rating: Substitute parts must have a drain-to-source voltage (Vdss) rating equal to or greater than 25 V to ensure safe operation within the original design envelope.
Operating Temperature Range: Substitute parts must support the -55°C to 150°C operating temperature range or a compatible subset.
Power Dissipation: Substitute parts must have power ratings sufficient for the application; higher power ratings provide additional design margin.

The substitute parts listed below meet these criteria and are classified as active products with current manufacturing status and improved compliance certifications.

Parameter Comparison

Parameter	BFR31LT1	MMBF5457	MMBF5484	MMBF5485	MMBF5486	MMBFJ108	MMBFJ110	MMBF4393LT1G
Manufacturer	onsemi	onsemi	onsemi	onsemi	onsemi	onsemi	onsemi	onsemi
FET Type	N-Channel JFET	N-Channel JFET	N-Channel JFET	N-Channel JFET	N-Channel JFET	N-Channel JFET	N-Channel JFET	N-Channel JFET
Package / Case	SOT-23-3	SOT-23-3	SOT-23-3	SOT-23-3	SOT-23-3	SOT-23-3	SOT-23-3	SOT-23-3
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Vdss / Voltage - Breakdown (V(BR)GSS)	25 V	25 V	25 V	25 V	25 V	25 V	25 V	30 V
Idss @ Vds (Vgs=0)	1 mA @ 10 V	1 mA @ 15 V	5 mA @ 15 V	10 mA @ 15 V	20 mA @ 15 V	80 mA @ 15 V	10 mA @ 15 V	5 mA @ 15 V
VGS off @ Id	2.5 V @ 0.5 nA	500 mV @ 10 nA	—	—	—	3 V @ 10 nA	4 V @ 10 nA	500 mV @ 10 nA
Ciss (Max) @ Vds	5 pF @ 10V	7 pF @ 15V	—	—	—	—	—	14 pF @ 15V
Power - Max	225 mW	350 mW	400 mW	400 mW	400 mW	350 mW	460 mW	225 mW
Operating Temperature	-55 to 150°C	-55 to 150°C	-55 to 150°C	-55 to 150°C	-55 to 150°C	-55 to 150°C	150°C	-55 to 150°C
Product Status	Obsolete	Active	Active	Active	Active	Active	Active	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

Primary Substitute: MMBF5457

The MMBF5457 is the most direct substitute for the BFR31LT1. Both parts share identical voltage ratings (25 V Vdss), matching package specifications (SOT-23-3), and compatible operating temperature ranges (-55°C to 150°C). The MMBF5457 offers improved power dissipation (350 mW versus 225 mW) and is classified as an active product with ROHS3 compliance, addressing the obsolescence and compliance limitations of the BFR31LT1.

Secondary Substitutes: MMBF5484, MMBF5485, MMBF5486

These RF JFET parts operate at 400 MHz and provide higher current ratings (5 mA, 10 mA, and 20 mA respectively) with increased power dissipation (400 mW). They are suitable for applications requiring higher frequency performance or greater current handling. All three maintain the 25 V voltage rating and SOT-23-3 package compatibility. These parts are active products with ROHS3 compliance.

Alternative Substitutes: MMBFJ108, MMBFJ110

The MMBFJ108 and MMBFJ110 are N-Channel JFETs in SOT-23-3 packages with 25 V voltage ratings and active product status. MMBFJ108 provides 80 mA drain current with 350 mW power dissipation, while MMBFJ110 offers 10 mA drain current with 460 mW power dissipation. Both are ROHS3 compliant. These parts are suitable for applications requiring higher current capacity than the original BFR31LT1.

Higher Voltage Alternative: MMBF4393LT1G

The MMBF4393LT1G is an N-Channel JFET with a 30 V voltage rating, providing additional design margin for applications with higher voltage requirements. It maintains the SOT-23-3 package and 225 mW power rating matching the original part. This part is active and ROHS3 compliant, making it suitable for designs requiring enhanced voltage headroom.

Frequently Asked Questions (FAQ)

Q: Can I directly replace BFR31LT1 with MMBF5457 without circuit modifications?

A: Yes. Both parts share identical voltage ratings (25 V), the same SOT-23-3 package, and compatible operating temperature ranges. The MMBF5457 provides higher power dissipation (350 mW versus 225 mW), which offers additional thermal margin. No circuit modifications are required for direct substitution.

Q: What is the key difference between MMBF5457 and MMBF5484?

A: The MMBF5457 is a general-purpose N-Channel JFET, while MMBF5484 is an RF JFET optimized for 400 MHz operation. MMBF5484 has higher drain current (5 mA versus 1 mA) and power dissipation (400 mW versus 350 mW). Select MMBF5484 for RF or high-frequency applications; use MMBF5457 for standard switching or amplification circuits.

Q: Why is MMBFJ110 listed with only 150°C maximum operating temperature instead of -55°C to 150°C?

A: The provided specification for MMBFJ110 indicates a maximum operating temperature of 150°C (TJ). Verify the complete temperature range with the manufacturer datasheet before selection if your application requires operation below room temperature.

Q: Are all substitute parts RoHS compliant?

A: Yes. All substitute parts listed (MMBF5457, MMBF5484, MMBF5485, MMBF5486, MMBFJ108, MMBFJ110, and MMBF4393LT1G) are ROHS3 compliant. The original BFR31LT1 is RoHS non-compliant, making these substitutes necessary for designs requiring RoHS compliance.

Q: Can I use MMBF4393LT1G as a drop-in replacement for BFR31LT1?

A: Yes, with the consideration that MMBF4393LT1G has a higher voltage rating (30 V versus 25 V). This provides additional design margin and is electrically compatible. The SOT-23-3 package and 225 mW power rating match the original part. No circuit modifications are required.

Q: What is the difference between MMBF5485 and MMBF5486?

A: Both are RF JFETs with 400 MHz operation and 25 V voltage ratings in SOT-23-3 packages. The primary difference is drain current: MMBF5485 is rated for 10 mA, while MMBF5486 is rated for 20 mA. Select MMBF5486 for applications requiring higher current handling.

Q: Which substitute part has the lowest drain current specification?

A: MMBF5457 has a drain current (Idss) of 1 mA at 15 V, matching the original BFR31LT1 specification of 1 mA at 10 V. This makes MMBF5457 the most direct electrical equivalent for applications sensitive to drain current characteristics.

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