onsemi MJF122

Overview

MJF122 from onsemi is an NPN complementary silicon power Darlington transistor in a TO-220 isolated package, designed for high-current switching and amplification where electrical isolation between mounting surface and heatsink is required. It delivers 5.0 A continuous collector current, sustains 100 VCEO(sus), achieves minimum DC current gain of 2000 at 3 A, and provides 4500 VRMS isolation per UL File #E69369 - used in industrial motor controls, relay drivers, and DC power supplies.

For engineers reviewing the MJF122 datasheet, pinout, applications, or equivalent options, key selection criteria include its electrically isolated TO-220 package, 100 V/5 A rating, 4.1°C/W junction-to-case thermal resistance, and compatibility with TIP122-based designs requiring enhanced isolation and reduced system cost.

Technical Context

The MJF122 integrates a monolithic Darlington pair with built-in base-emitter resistor network, enabling high DC current gain (hFE ≥ 2000 @ IC = 3 A) while maintaining low saturation voltage (VCE(sat) ≤ 2 V @ IC = 3 A, IB = 12 mA). Its fully insulated package eliminates need for isolating washers, supporting direct mounting to grounded heatsinks without compromising safety or creepage distance.

It operates across −65°C to +150°C junction temperature range, with thermal resistance RJC = 4.1°C/W and RJA = 62.5°C/W, and meets UL recognition for 3500 VRMS isolation (tested to 4500 VRMS per Figure 14). The device exhibits secondary breakdown-limited safe operating area up to 30 W at TC = 25°C, derating linearly above that temperature.

Key Specifications

Pinout & Package

Package: TO-220 FullPAK (Case 221D-02, Style 2), fully electrically isolated plastic housing with metal tab mounted to collector. Mounting screw torque must not exceed 10 in·lbs to preserve isolation integrity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN Darlington switching applications.

Compared with TIP122 and BDW53C, the MJF122 uniquely combines certified 4500 VRMS isolation, 2000 min hFE, and TO-220 mechanical compatibility - enabling drop-in replacement in legacy TIP122 layouts *only* when isolation is added externally, whereas MJF122 removes that requirement entirely.

Availability

MJF122 is available at Aetrix Electronics and suitable for industrial motor control, DC power supply regulation, and relay/solenoid driver applications requiring stable component supply, long lifecycle support, and traceable sourcing for production programs.

Supply support for MJF122 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, and IoT markets.

The MJF122 belongs to onsemi's Complementary Power Darlingtons product line, engineered specifically for electrically isolated high-current switching in safety-critical industrial systems where mounting surface isolation is mandatory.

FAQ

What is the maximum continuous collector current rating for the MJF122?

The MJF122 is rated for 5.0 A continuous collector current (IC) at TC = 25°C. Derating applies above 25°C at 0.24 W/°C for junction-to-case operation. This rating assumes proper heatsinking and adherence to the 10 in·lb maximum mounting torque to maintain isolation integrity. The MJF122 maintains this current capability within its safe operating area up to 150°C junction temperature.

Does the MJF122 require an insulating washer when mounted to a heatsink?

No, the MJF122 does not require an insulating washer. Its TO-220 FullPAK package features a fully electrically isolated metal tab bonded to the collector, validated for 4500 VRMS isolation. This design eliminates the need for mica or silicone insulators, reducing assembly complexity and improving thermal reliability. However, mounting torque must remain ≤10 in·lbs to prevent cracking and isolation loss - a critical constraint specified in the official MJF122 datasheet.

How does the MJF122 compare to the TIP122 in terms of electrical performance and packaging?

The MJF122 matches the TIP122's core electrical specs - 100 VCEO(sus), 5 A IC, and similar VCE(sat) - but differs critically in packaging: MJF122 uses an electrically isolated TO-220 variant with UL recognition (File #E69369), while TIP122 is non-isolated. As a result, MJF122 enables direct heatsink mounting without washers, whereas TIP122 requires external isolation. Both share pinout compatibility (Base-Collector-Emitter), but MJF122's isolation adds safety margin for industrial certifications.

What is the minimum DC current gain (hFE) of the MJF122 and under what conditions is it specified?

The MJF122 guarantees a minimum DC current gain (hFE) of 2000 at IC = 3 A and VCE = 3 VDC, measured at TC = 25°C. This high gain enables low base drive requirements - typically ≤1.5 mA for full saturation at 3 A collector current. The datasheet also specifies hFE ≥ 1000 at IC = 0.5 A, confirming strong performance across its operational range. Gain remains usable down to −65°C and up to 150°C, though values decrease at temperature extremes as shown in Figure 8.

Can the MJF122 be used in complementary pairs with the MJF127 for push-pull amplifier designs?

Yes, the MJF122 (NPN) and MJF127 (PNP) are explicitly designed as complementary power Darlingtons and share identical TO-220 isolated packaging, voltage/current ratings (100 V, 5 A), and thermal characteristics (RJC = 4.1°C/W). Their matched gain profiles and isolation properties make them suitable for Class AB audio output stages, H-bridge motor drivers, and symmetrical DC-DC converter topologies where balanced conduction and shared heatsink mounting are required without additional isolation hardware.