onsemi MJE371

Overview

MJE371 from onsemi is a plastic medium-power PNP silicon transistor designed for general-purpose amplifier and switching circuits, with 40 V_CEO, 4.0 A_C continuous collector current, 40 W total power dissipation at T_C = 25°C, and complementary pairing to NPN MJE521 - recommended for 5–20 W audio amplifiers using complementary symmetry topology.

For engineers reviewing the MJE371 datasheet, pinout, applications, or equivalent options, key selection considerations include safe operating area (SOA) limits at T_J(pk) = 150°C, thermal resistance R_JC = 3.12°C/W, V_EB = 4.0 Vdc maximum, h_FE ≥ 40 at I_C = 1.0 A, and TO-225 package mechanical compatibility.

Technical Context

The MJE371 operates as a medium-power PNP bipolar junction transistor in linear amplification and hard-switching modes, supporting DC current gain (h_FE) ≥ 40 under I_C = 1.0 A, V_CE = 1.0 V conditions, and sustaining V_CEO(sus) = 40 Vdc at I_C = 100 mA with zero base drive.

Its safe operating area is constrained by both thermal limits (T_J ≤ 150°C) and second breakdown, with pulse SOA validated for duty cycles ≤10% and pulse widths up to 100 s; R_JC = 3.12°C/W enables direct heatsink mounting via the metal tab (pins 2 & 4).

Key Specifications

Pinout & Package

Package: TO-225 (Case 77-09, Style 1), plastic molded with metal tab (collector-connected), Pb-free (MJE371G), 3-pin configuration (pins 1, 2, 3, 4 - pins 2 & 4 internally joined to collector).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJE371, MJE2955G offers greater voltage headroom but reduced DC gain consistency, while BD139 provides higher voltage rating in a smaller package but lacks current and thermal capacity - neither is pin-compatible, and both require PCB layout changes and SOA revalidation.

Availability

MJE371 is available at Aetrix Electronics and suitable for audio amplifier output stages, DC motor drivers, linear voltage regulators, and industrial relay interfaces requiring stable component supply and long-term manufacturability.

Supply support for MJE371 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 focused on energy-efficient electronics, delivering high-performance analog, logic, discrete, and power management solutions.

The MJE371 belongs to onsemi's legacy medium-power bipolar transistor product line, engineered specifically for cost-sensitive, thermally demanding linear and switching applications in audio, industrial controls, and power conversion.

FAQ

What is the maximum continuous collector current rating for the MJE371?

The MJE371 has a maximum continuous collector current (I_C) rating of 4.0 Adc at T_C = 25°C. This rating assumes adequate heatsinking to maintain case temperature; derating is required above 25°C at 320 mW/°C. The device also supports 8.0 A peak collector current for short-duration pulses, subject to SOA constraints shown in Figure 1 of the datasheet. Always verify thermal design margins using R_JC = 3.12°C/W when applying the MJE371 in production circuits.

Is the MJE371 pin-compatible with the MJE521?

No - the MJE371 is a PNP transistor while the MJE521 is its complementary NPN counterpart; they share identical TO-225 packaging and mechanical footprint but have opposite polarity and reversed pin functions (e.g., emitter/base/collector assignments differ). Their electrical symmetry enables use in complementary amplifier stages, but they are not interchangeable on the same PCB footprint. The MJE371 pinout is Emitter (pin 1), Collector (pins 2 & 4), Base (pin 3).

Does the MJE371 require a heatsink in typical 10 W audio amplifier applications?

Yes - even in 10 W audio amplifier output stages, the MJE371 dissipates significant heat during quiescent and dynamic operation. With R_JC = 3.12°C/W and a maximum junction temperature of 150°C, a heatsink is essential to limit T_C and ensure reliability. For example, at 15 W dissipation and ambient 50°C, a heatsink with ≤ 4.5°C/W thermal resistance (including interface) is required. The metal tab (collector) must be electrically isolated if mounted to a grounded heatsink.

What does the "G" suffix in MJE371G signify?

The "G" suffix in MJE371G indicates a Pb-free (lead-free) and RoHS-compliant version of the device, per onsemi's environmental policy. It denotes compliance with Directive 2011/65/EU and related restrictions on hazardous substances. The "G" variant uses matte tin lead finish and conforms to JEDEC J-STD-020 moisture sensitivity level (MSL) requirements. Non-G versions are obsolete; all currently shipped MJE371 devices are MJE371G.

Can the MJE371 be used in switching power supplies?

The MJE371 is rated for switching applications per its datasheet, but it is optimized for medium-speed linear and quasi-linear operation - not high-frequency SMPS. Its storage time (t_s) and fall time (t_f) are not specified, and safe operating area limits favor lower-frequency (<100 kHz), higher-current duty cycles. For flyback or forward converter switches, MOSFETs or faster BJTs like the MJD127 are preferred. The MJE371 remains appropriate for low-frequency PWM motor drives or relay control where switching speed is secondary to current and ruggedness.