onsemi MJF31C

Overview

MJF31C from onsemi is an NPN silicon power transistor in TO-220 FullPak package, rated for 100 V_CEO, 3.0 A continuous collector current, and 28 W power dissipation at T_C = 25°C, designed for general-purpose amplifier and switching applications in isolated-package industrial power supplies and motor drivers.

For engineers reviewing the MJF31C datasheet, pinout, applications, or equivalent options, this page delivers verified electrical specs, thermal derating behavior, safe operating area limits, saturation voltage performance under 3.0 A load, and real-world switching time data (t_r ≤ 7.0 ns, t_f < 15 ns) critical for high-reliability power stage design.

Technical Context

The MJF31C operates as a medium-power NPN bipolar junction transistor with DC current gain (h_FE) of 25–50 at I_C = 1.0 A and 10–50 at I_C = 3.0 A, supporting linear amplification and hard-switching roles. Its V_CE(sat) ≤ 1.2 V at I_C = 3.0 A and I_B = 375 mA ensures low conduction loss in saturated switch configurations.

Thermally, it features R_θJC = 4.46°C/W and R_θJA = 62.5°C/W, enabling direct heatsink mounting while maintaining junction temperature within –65°C to +150°C range. Its unclamped inductive load energy rating of 32 mJ supports robust operation in relay driving and solenoid control circuits.

Key Specifications

Pinout & Package

Package: TO-220 FullPak (Case 221D-03), thermally enhanced plastic package with insulated tab, UL-recognized for 3500 V_RMS isolation between collector and mounting surface.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN power transistor applications.

Compared with MJE13003 and BD139, the MJF31C uniquely combines UL-recognized 3500 V_RMS isolation, 28 W power handling at T_C = 25°C, and validated 32 mJ unclamped inductive energy tolerance-making it the only option among the three qualified for industrial auxiliary supplies requiring reinforced insulation and high reliability.

Availability

MJF31C is available at Aetrix Electronics and suitable for industrial power supply auxiliary circuits, DC motor speed control stages, relay and solenoid drivers, linear audio amplifier output stages, and isolated gate driver bias generation requiring stable component supply and long-term lifecycle support.

Supply support for MJF31C includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power management, analog, sensors, and connectivity solutions for automotive, industrial, cloud, medical, and IoT markets.

The MJF31C belongs to onsemi's complementary silicon plastic power transistor family designed specifically for isolated-package applications demanding high-voltage blocking, robust thermal performance, and safety-certified insulation in industrial control and power conversion systems.

FAQ

What is the maximum continuous collector current rating for MJF31C?

The MJF31C is rated for 3.0 Adc continuous collector current at case temperature T_C = 25°C. Derating applies above 25°C at 0.22 W/°C, meaning usable current drops to approximately 2.0 A at T_C = 70°C. This rating assumes proper heatsinking per the TO-220 FullPak package's R_θJC = 4.46°C/W specification. The MJF31C must not exceed this limit to avoid thermal runaway or second breakdown.

Does MJF31C have UL recognition, and what does that mean for my design?

Yes, the MJF31C is UL Recognized under File #E69369 for 3500 V_RMS isolation between collector and mounting surface. This means the TO-220 FullPak package's insulated tab meets reinforced insulation requirements per UL 60950-1 and UL 62368-1. In your design, this eliminates the need for additional insulating hardware when mounting the MJF31C directly to a grounded heatsink in isolated auxiliary supplies or gate drivers.

What is the typical V_CE(sat) of MJF31C under full-load conditions?

The MJF31C guarantees V_CE(sat) ≤ 1.2 Vdc at I_C = 3.0 Adc and I_B = 375 mAdc, per the datasheet's "ON CHARACTERISTICS" table. At lower currents (e.g., I_C = 1.0 A), V_CE(sat) typically falls to ~0.8 V. This low saturation voltage directly reduces conduction losses-critical for efficiency in motor drivers and power supply regulators using the MJF31C.

Can MJF31C be used in switching applications above 100 kHz?

The MJF31C has a minimum f_T of 3.0 MHz, but its practical switching frequency is limited by stored charge and minority carrier lifetime-not just f_T. Measured turn-on time (t_r) is ≤7.0 ns and turn-off time (t_f) < 15 ns, supporting clean edges up to ~200 kHz in hard-switched topologies. However, for sustained operation above 100 kHz, thermal management and base drive strength become critical; the MJF31C remains viable if average power dissipation stays within derated limits.

How does the unclamped inductive load energy rating of MJF31C affect relay driving?

The MJF31C's 32 mJ unclamped inductive load energy rating (tested at I_C = 1.8 A, L = 20 mH, V_CC = 10 V) ensures reliable operation when switching relays and solenoids without external snubbers. For example, a 24 V, 100 Ω relay coil (I ≈ 240 mA, L ≈ 15 mH) generates ~4.3 mJ of stored energy-well below the MJF31C's 32 mJ limit. This rating directly enables simplified, cost-effective relay driver designs using the MJF31C.