onsemi MSD42T1G

Overview

MSD42T1G from onsemi is an NPN silicon planar transistor designed for general-purpose amplifier and high-voltage switching applications, featuring 300 V collector-emitter breakdown voltage (V_(BR)CEO), 150 mA continuous collector current (I_C), and 450 mW power dissipation in SC−59 surface-mount package-used in flyback snubber circuits, relay drivers, and low-power HV amplifiers.

For engineers reviewing the MSD42T1G datasheet, pinout, applications, or equivalent options, key selection criteria include high-voltage blocking capability (300 V), DC current gain range (25–40 at I_C = 1–30 mA), saturation voltage ≤0.5 V at I_C/I_B = 10, thermal resistance of 274 °C/W, and Pb-free SC−59 packaging for space-constrained industrial controls.

Technical Context

This device operates as a discrete NPN bipolar junction transistor with fixed junction architecture optimized for stable high-voltage operation up to 300 V across collector-base and collector-emitter terminals. Its planar construction ensures consistent parameter distribution across production lots and supports reliable performance in intermittent switching and linear amplification modes.

The SC−59 package enables low-profile surface mounting with defined thermal path characteristics (R_JA = 274 °C/W on FR-4 with 10 mm² copper), while its specified cutoff currents (I_CBO, I_EBO ≤ 0.1 µA) confirm suitability for high-impedance bias networks and low-leakage signal conditioning stages.

Key Specifications

Pinout & Package

The MSD42T1G is housed in the SC−59 (Case 318D, Style 1) surface-mount package, measuring 2.90 × 1.50 × 1.15 mm with 1.90 mm lead pitch. It features gull-wing leads compatible with standard reflow profiles and RoHS-compliant Pb-free finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA42 and ZTX413, the MSD42T1G offers superior thermal performance (274 °C/W vs. ≥357 °C/W) and surface-mount compatibility while maintaining identical 300 V blocking capability-making it optimal for automated production of compact, thermally demanding industrial controls.

Availability

MSD42T1G is available at Aetrix Electronics and suitable for relay driver circuits, flyback snubber networks, low-power HV amplifiers, and industrial sensor interfaces requiring stable component supply and long-term manufacturability.

Supply support for MSD42T1G 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 power, analog, sensing, and connectivity solutions for automotive, industrial, and cloud infrastructure markets.

The MSD42T1G belongs to onsemi's general-purpose high-voltage transistor product line, engineered specifically for cost-sensitive, space-constrained applications needing reliable 300 V switching and amplification without premium packaging or process complexity.

FAQ

What is the maximum collector-emitter voltage rating for the MSD42T1G?

The MSD42T1G 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 applies under DC conditions and defines the absolute maximum voltage the device can block in open-circuit switch applications. Exceeding this voltage risks irreversible avalanche failure. The MSD42T1G must be operated within this limit in all designs, including transient surges.

Does the MSD42T1G support surface-mount reflow assembly?

Yes, the MSD42T1G uses the SC−59 (Case 318D) surface-mount package with gull-wing leads and Pb-free finish, fully compatible with standard lead-free reflow profiles (J-STD-020). Its 2.90 × 1.50 mm footprint and thermal resistance specification assume mounting on FR-4 with 10 mm² copper area, making it suitable for automated PCB assembly lines serving industrial and consumer electronics.

What is the DC current gain (h_FE) range for the MSD42T1G?

The MSD42T1G exhibits h_FE of 25–40 when measured at V_CE = 10 V and I_C = 1.0 mA (h_FE1), and 40 minimum at V_CE = 10 V and I_C = 30 mA (h_FE2). These values are production-tested minimums-not typicals-and define base drive requirements for saturation. Designers must verify gain behavior across temperature and current in final circuit validation using the MSD42T1G.

Can the MSD42T1G replace the MPSA42 in existing designs?

The MSD42T1G shares identical 300 V voltage ratings and similar gain/switching characteristics with the MPSA42 but differs in package (SC−59 vs. TO-92) and pinout (Base-Emitter-Collector vs. Emitter-Base-Collector). Direct replacement requires PCB layout revision. While electrically comparable, the MSD42T1G is not a drop-in substitute; redesign is needed to accommodate surface-mount placement and revised trace routing for the MSD42T1G.

What is the thermal resistance junction-to-ambient (R_JA) for the MSD42T1G?

The MSD42T1G has a specified R_JA of 274 °C/W when mounted on FR-4 PCB with 10 mm² of 1 oz. copper per JEDEC standard test conditions. This value assumes no additional heatsinking and defines how much the junction temperature rises above ambient per milliwatt of dissipated power. For continuous 450 mW operation, ambient must remain below ~30 °C to avoid exceeding the 150 °C max junction temperature-derating is required at higher temperatures.