onsemi MJF18008

Overview

MJF18008 from onsemi is an isolated TO-220AB NPN bipolar power transistor designed for high-voltage switching in 220 V line-operated switch-mode power supplies and electronic light ballasts. It delivers 8.0 A continuous collector current, sustains 450 Vdc collector-emitter voltage, and features UL recognition at 3500 VRMS isolation - enabling safe operation in grounded heatsink configurations.

For engineers reviewing the MJF18008 datasheet, pinout, applications, or equivalent options, key selection criteria include RMS isolation rating (3500 VRMS), thermal resistance (2.78 °C/W junction-to-case), fast switching performance (ton ≤ 180 ns, toff ≤ 2.5 µs), low VCE(sat) (0.3–0.8 V), and high hFE (6.0–20 at IC = 4.5 A).

Technical Context

The MJF18008 uses a state-of-the-art die optimized for hard-switched, high-voltage SMPS topologies where rapid turn-off without tail current is critical. Its isolated package eliminates need for insulating hardware while maintaining creepage/strike distances compliant with UL File #E69369.

It operates with base-driven saturation control (IC/IB = 5–10), supports resistive and inductive loads up to 300 V clamp, and exhibits flat DC current gain across temperature (hFE ≥ 6.0 at TC = 125 °C, IC = 4.5 A). Dynamic saturation voltage remains stable under pulsed conditions (VCE(dsat) ≤ 11.5 V at 1 s, 3.5 V at 3 s).

Key Specifications

Pinout & Package

Package: TO-220 Fullpak (Case 221D), fully isolated plastic package with electrically insulated tab. Mounting via screw or clip per Figures 22a–c and 23a–b; max torque 10 in·lbs to preserve isolation integrity.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJE18008G and ST13007D, the MJF18008 uniquely combines UL-recognized 3500 VRMS isolation, 450 V sustain voltage, and 8 A capability in a single TO-220 Fullpak - making it the only option for safety-certified, grounded-heatsink SMPS without added insulation layers or derating.

Availability

MJF18008 is available at Aetrix Electronics and suitable for switch-mode power supply design, electronic ballast development, and industrial AC-DC conversion requiring stable component supply, long-term lifecycle support, and certified isolation performance.

Supply support for MJF18008 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 power, analog, sensor, and logic solutions for automotive, industrial, and cloud infrastructure markets.

The MJF18008 belongs to onsemi's high-voltage bipolar power transistor family engineered specifically for energy-efficient, safety-compliant switching power supplies and lighting ballasts - emphasizing isolation integrity, thermal reliability, and consistent parametric performance.

FAQ

What is the maximum mounting torque for the MJF18008 to maintain its 3500 VRMS isolation rating?

The MJF18008 must not exceed 10 in·lbs of screw mounting torque to prevent cracking of the plastic case and loss of isolation integrity. Laboratory testing shows torque >10 in·lbs risks compromising the UL-recognized 3500 VRMS rating per Test No. 1 (Figure 22b). Proper compression washers and 6–8 in·lbs torque are recommended for optimal thermal and electrical performance. This specification applies exclusively to the MJF18008 in its TO-220 Fullpak (Case 221D) configuration.

Does the MJF18008 require a base turn-off coil like older bipolar transistors?

No, the MJF18008 does not require a base turn-off coil. Its die design eliminates current tail during turn-off, enabling clean, fast switching with simple resistor-based base drive. This is confirmed in the datasheet Features section and validated by measured toff ≤ 2.5 µs under inductive load. The absence of tail current reduces driver complexity and improves efficiency in MJF18008-based SMPS designs.

How does the thermal resistance of the MJF18008 compare to the MJE18008, and what does that mean for heatsink selection?

The MJF18008 has a junction-to-case thermal resistance (RJC) of 2.78 °C/W, versus 1.0 °C/W for the non-isolated MJE18008. This means the MJF18008 requires a larger or more efficient heatsink to dissipate its 45 W maximum power at TC = 25 °C. For example, achieving 60 °C case temperature with 40 W dissipation requires a heatsink + interface resistance of ≤ 1.22 °C/W for the MJF18008 - a 2.7× stricter requirement than the MJE18008. This trade-off enables grounded heatsink use without insulation.

Can the MJF18008 replace the MJE18008 in an existing design without layout changes?

No - the MJF18008 cannot serve as a direct drop-in replacement for the MJE18008 due to different pinouts (Style 2 vs. Style 1) and isolation requirements. The MJF18008 uses Base–Emitter–Collector (pin 1–2–3), while the MJE18008 uses Base–Collector–Emitter. Additionally, the MJF18008's isolated tab demands revised mechanical mounting and grounding strategy. Any migration requires PCB layout revision and thermal validation. The MJF18008 is a functionally distinct part optimized for isolated-system integration.

What is the guaranteed minimum hFE for the MJF18008 at elevated temperature and high current?

The MJF18008 guarantees hFE ≥ 6.0 at IC = 4.5 A, VCE = 1.0 Vdc, and TC = 125 °C - a critical parameter for stable base drive design in hot environments. This value is specified in the Electrical Characteristics table (page 2) and confirmed across production lots. Unlike many legacy transistors, the MJF18008 maintains this gain with minimal degradation up to 150 °C junction temperature, supporting reliable operation in compact, thermally constrained enclosures.