onsemi MJE3439G

Overview

MJE3439G from onsemi is an NPN silicon high-voltage power transistor designed for line-operated equipment requiring high f_T (15 MHz), with V_CEO = 350 V, I_C = 0.3 A, P_D = 15 W at T_C = 25°C, and low output capacitance (C_ob ≤ 10 pF). It serves as a switching or linear amplifier in high-voltage AC/DC power supplies and CRT horizontal deflection circuits.

For engineers reviewing the MJE3439G datasheet, pinout, applications, or equivalent options, key selection considerations include its TO-225 package with emitter-base-collector pinout, high-voltage blocking capability, DC current gain range (h_FE = 15–200), thermal resistance (R_θJC = 8.33°C/W), and safe operating area limits under pulse and continuous conditions.

Technical Context

The MJE3439G operates as a single NPN bipolar junction transistor optimized for high-voltage switching applications where fast turn-off and low storage time are critical. Its f_T of 15 MHz enables stable gain at medium frequencies, while low C_ob minimizes Miller effect in high-speed switching.

It features a rugged SOA profile supporting up to 350 V V_CE at 0.05 A and 100 V at 0.3 A under DC conditions, with derating to zero power at 150°C case temperature. The device uses epitaxial base construction to achieve high V_CB (450 V) and low leakage (I_CEO ≤ 20 µA).

Key Specifications

Pinout & Package

Package: TO-225 (Case 77-09, Style 1), plastic through-hole package with metal tab connected to collector (pins 2 and 4), 3-pin configuration, Pb-free compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJE13003G and BU2508AX, the MJE3439G offers optimal balance of high f_T, moderate voltage rating, and compact TO-225 footprint-making it preferred for space-constrained, medium-frequency (<500 kHz), 20–60 W power stages where gain-bandwidth and thermal density matter more than raw current handling.

Availability

MJE3439G is available at Aetrix Electronics and suitable for switch-mode power supplies, CRT deflection circuits, industrial relay drivers, and AC line surge protection systems requiring stable component supply and long-term manufacturability.

Supply support for MJE3439G 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 delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The MJE3439G belongs to onsemi's high-voltage bipolar power transistor product line, engineered specifically for reliability-critical line-operated equipment where high V_CEO, controlled SOA, and consistent f_T performance are essential.

FAQ

What is the maximum collector-emitter voltage rating for the MJE3439G?

The MJE3439G has a maximum collector-emitter sustaining voltage (V_CEO(sus)) of 350 Vdc at I_C = 5.0 mA and I_B = 0. This rating is verified per JEDEC test conditions and defines the absolute upper limit for DC or repetitive pulse operation without breakdown. Exceeding this voltage risks irreversible avalanche failure. The MJE3439G must be used with appropriate voltage margin-typically ≤ 80% of 350 V-in real-world designs accounting for transients and ringing.

Does the MJE3439G have a built-in base-emitter resistor or ESD protection diode?

No, the MJE3439G is a bare-die NPN bipolar transistor with no integrated base-emitter resistor or on-chip ESD protection diodes. It requires external base current limiting and discrete ESD protection (e.g., series resistor + parallel TVS) in sensitive environments. This design preserves full control over biasing and switching dynamics but places responsibility on the circuit designer to implement proper drive and protection networks for the MJE3439G.

Can the MJE3439G be used in linear amplifier configurations?

Yes, the MJE3439G is qualified for linear operation with specified h_FE (15–200), V_BE(on) (≤0.8 V), and SOA curves covering DC and pulse conditions. Its low C_ob and high f_T support stable mid-band amplification, as seen in CRT deflection yoke drivers. However, linear use demands strict adherence to the derating curve (Figure 1) and SOA boundaries (Figure 2); sustained operation above 10 W at T_C > 70°C requires active cooling to prevent thermal runaway in the MJE3439G.

What is the thermal resistance from junction to case for the MJE3439G?

The MJE3439G has a specified thermal resistance from junction to case (R_θJC) of 8.33°C/W. This value assumes proper mechanical mounting of the TO-225 metal tab to a heatsink with thermal interface material. To maintain T_J ≤ 150°C at full 15 W dissipation, the total system thermal resistance (R_θJC + R_θCS + R_θSA) must remain ≤ 6.67°C/W-requiring a heatsink with R_θSA ≤ 5.0°C/W when using standard thermal paste and mounting pressure for the MJE3439G.

Is the MJE3439G pin-compatible with other TO-225 NPN transistors like the MJE340?

No, the MJE3439G is not pin-compatible with the MJE340. While both use TO-225 packages, the MJE340 follows Style 3 (pin 1 = base, pin 2/4 = collector, pin 3 = emitter), whereas the MJE3439G uses Style 1 (pin 1 = emitter, pin 2/4 = collector, pin 3 = base). Swapping them without PCB revision will reverse emitter-base polarity and cause immediate failure. Always verify pinout diagrams in the official MJE3439G datasheet before board layout or replacement.