onsemi MPSA42G

Overview

MPSA42G from onsemi is an NPN silicon high-voltage general-purpose transistor in TO-92 package, rated for 300 V_CEO, 500 mA continuous collector current, and 625 mW power dissipation at 25°C ambient. It delivers DC current gain (h_FE) ≥25 at I_C = 1.0 mA and supports switching and linear amplification in high-voltage interface circuits.

For engineers reviewing the MPSA42G datasheet, pinout, applications, or equivalent options, key selection criteria include its 300 V_CEO rating, TO-92 leaded package compatibility with through-hole prototyping and legacy industrial controls, thermal resistance of 200°C/W (junction-to-ambient), and verified performance across −55°C to +150°C junction temperature range.

Technical Context

The MPSA42G operates as a discrete NPN bipolar junction transistor optimized for high-voltage switching and amplification where breakdown voltage exceeds standard signal transistors. Its V_(BR)CEO = 300 V and V_(BR)CBO = 300 V enable use in flyback snubbers, relay drivers, and HV bias supplies up to 250 V DC rail.

It exhibits h_FE = 25–40 across I_C = 1–30 mA, V_CE(sat) ≤ 0.5 V at I_C/I_B = 10, and f_T = 50 MHz - confirming suitability for medium-speed switching (≤1 MHz) and low-noise preamplifier stages in instrumentation front-ends.

Key Specifications

Pinout & Package

Package: TO-92 (Case 29-11), Pb-free, through-hole mounting with bent leads. Dimensions per ON Semiconductor specification: 4.45–5.20 mm height, 4.32–5.33 mm width, 3.18–4.19 mm depth.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MMBT4401LT1G and 2N5551, the MPSA42G uniquely balances 300 V capability, TO-92 through-hole compatibility, and predictable h_FE behavior across temperature - making it the default choice for legacy-replacement and high-reliability HV interface designs.

Availability

MPSA42G is available at Aetrix Electronics and suitable for industrial relay drivers, switch-mode power supply snubbers, LED string bias control, and high-voltage signal amplifiers requiring stable component supply across long-lifecycle programs.

Supply support for MPSA42G 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 power, analog, sensing, and connectivity solutions for automotive, industrial, cloud, medical, and IoT applications.

The MPSA42G belongs to onsemi's high-voltage discrete transistor product line, engineered specifically for robustness in industrial controls, power conversion, and legacy system upgrades where reliability under sustained high-voltage stress is mandatory.

FAQ

What is the maximum collector-emitter voltage rating for the MPSA42G?

The MPSA42G has a guaranteed minimum collector-emitter breakdown voltage V_(BR)CEO of 300 V at I_C = 1.0 mA and I_B = 0. This rating allows safe operation in circuits with up to 250 V DC supply rails while maintaining design margin against transients. The MPSA42G must not be operated beyond this limit without external clamping or derating per thermal conditions.

Does the MPSA42G support surface-mount assembly?

No, the MPSA42G uses a TO-92 through-hole package with bent leads and is not compatible with standard SMT reflow processes. It requires wave soldering, hand soldering, or press-fit insertion. For surface-mount alternatives, consider the NSS40501MR6T1G (V_CEO = 400 V, SOT-23), but note that its pinout and thermal behavior differ significantly from the MPSA42G.

What is the typical DC current gain (h_FE) of the MPSA42G at 10 mA collector current?

At I_C = 10 mA and V_CE = 10 V, the MPSA42G exhibits h_FE between 40 and 120 depending on unit variation and temperature. The datasheet guarantees a minimum of 40 under those conditions. Designers should verify actual h_FE in their circuit context, as the MPSA42G's gain decreases at both low (<1 mA) and high (>100 mA) current extremes.

Can the MPSA42G replace the MPSA43 in a circuit?

The MPSA42G and MPSA43 are pin-compatible but not functionally interchangeable without review: the MPSA43 has V_CEO = 200 V and V_(BR)CBO = 200 V versus 300 V for the MPSA42G. Substituting MPSA42G for MPSA43 is safe if voltage stress exceeds 200 V; substituting MPSA43 for MPSA42G risks breakdown in 250–300 V applications. Always validate voltage margins before cross-substitution of the MPSA42G.

What is the thermal resistance junction-to-ambient (R_JA) for the MPSA42G in free-air conditions?

The MPSA42G has a maximum R_JA of 200°C/W when mounted on a standard FR-4 PCB with no added copper pour or airflow. This value assumes the TO-92 package is suspended in still air. In practice, adding 1 in² of 2-oz copper connected to the emitter pad reduces R_JA to ~120°C/W. Thermal design must ensure junction temperature stays below +150°C under worst-case power dissipation of the MPSA42G.