J108 JFET N-Channel Transistor Equivalent & Substitute Parts

Part Overview

The J108 is an N-channel JFET transistor manufactured by onsemi, rated for 25 V breakdown voltage with a maximum power dissipation of 625 mW in a through-hole TO-92-3 package. The device is classified as obsolete, making identification of functionally equivalent alternatives necessary for ongoing design support and production continuity. Substitute parts must maintain electrical performance across drain current, gate-source voltage characteristics, and thermal operating range while accommodating different mounting technologies.

Substiute Parts

J108

onsemiIn Stock: 3420J108 Datasheet

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MMBFJ108

onsemiIn Stock: 1197MMBFJ108 Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the J108 is determined by matching the following electrical and mechanical criteria:

Electrical Matching Parameters:

• FET Type: N-Channel (required match)
• Voltage - Breakdown (V(BR)GSS): 25 V (required match)
• Current - Drain (Idss) @ Vds (Vgs=0): 80 mA @ 15 V (required match)
• Voltage - Cutoff (VGS off) @ Id: 3 V @ 10 nA (required match)
• Resistance - RDS(On): 8 Ohms (required match)
• Operating Temperature Range: -55°C to 150°C (required match)

Mechanical Considerations:

• Package / Case: Substitutes may differ in mounting technology (through-hole versus surface-mount) provided the electrical parameters remain identical
• Power - Max: Substitutes with equal or greater power rating are acceptable

The MMBFJ108 meets all electrical specifications while utilizing surface-mount SOT-23-3 packaging instead of through-hole TO-92-3 technology.

Parameter Comparison

Engineering Selection Recommendations

The MMBFJ108 is a direct electrical equivalent to the J108 across all specified drain current, gate-source voltage, breakdown voltage, and on-resistance parameters. The primary distinction is packaging technology: the J108 uses through-hole TO-92-3 mounting, while the MMBFJ108 uses surface-mount SOT-23-3 technology.

The MMBFJ108 is classified as Active product status, ensuring ongoing availability and manufacturing support, whereas the J108 is Obsolete. Both devices operate across the identical temperature range (-55°C to 150°C) and share REACH Unaffected and EAR99 compliance classifications.

The MMBFJ108 has a lower maximum power rating (350 mW versus 625 mW). Applications requiring thermal dissipation near or exceeding 350 mW must evaluate whether the reduced power budget is acceptable for the specific circuit implementation.

Frequently Asked Questions (FAQ)

Q: Can the MMBFJ108 replace the J108 in existing through-hole PCB designs?

A: Direct PCB footprint replacement is not possible due to different mounting technologies. The J108 requires through-hole pads, while the MMBFJ108 requires surface-mount pads. PCB redesign or use of adapter modules is necessary.

Q: Are the electrical characteristics identical between J108 and MMBFJ108?

A: Yes. Both devices share identical specifications for breakdown voltage (25 V), drain current (80 mA @ 15 V), gate-source cutoff voltage (3 V @ 10 nA), and on-resistance (8 Ohms). Operating temperature range is also identical (-55°C to 150°C).

Q: What is the significance of the lower power rating on the MMBFJ108?

A: The MMBFJ108 is rated for 350 mW maximum power dissipation compared to 625 mW for the J108. Circuits dissipating power within the 350 mW limit are unaffected. Applications approaching or exceeding 350 mW require thermal analysis to confirm the substitute is suitable.

Q: Why is the J108 classified as Obsolete?

A: Obsolete status indicates the manufacturer has discontinued production. The MMBFJ108, classified as Active, represents the current production equivalent and is recommended for new designs and ongoing production support.

Q: Are there compliance or certification differences between the two parts?

A: Both devices share identical REACH Unaffected and EAR99 classifications. The MMBFJ108 carries RoHS3 Compliant status, providing additional environmental compliance documentation.