onsemi MSD42SWT1

Overview

MSD42SWT1 from onsemi is an NPN silicon planar transistor designed for general-purpose amplifier and high-voltage switching applications, featuring V(BR)CEO = 300 Vdc, IC = 150 mAdc, hFE = 25–200 (at IC = 1.0–30 mAdc), VCE(sat) ≤ 0.5 Vdc (IC = 200 mAdc, IB = 2.0 mAdc), and housed in SC-70/SOT-323 package. It serves in flyback snubber circuits, relay drivers, and low-power HV signal conditioning stages.

For engineers reviewing the MSD42SWT1 datasheet, pinout, applications, or equivalent options, key selection considerations include its 300 V breakdown rating, SOT-323 thermal derating behavior, DC current gain variation across operating current, and compatibility with low-power surface-mount PCB layouts requiring high-voltage isolation.

Technical Context

This device operates as a single NPN bipolar junction transistor with fixed emitter-base and collector-base junction structures optimized for stable high-voltage blocking. Its design supports linear amplification at low collector currents (1–30 mA) and saturated switching up to 150 mA continuous, with thermal limits defined by FR-4 board mounting per Note 1.

The SC-70 package imposes strict power dissipation constraints (PD = 150 mW at TA = 25°C), requiring careful layout for heat spreading and trace width management. Cutoff leakage (ICBO ≤ 0.1 µA at VCB = 300 V) and gain consistency are validated under pulsed test conditions (300 µs, 2% duty cycle).

Key Specifications

Pinout & Package

MSD42SWT1 is packaged in SC-70 (SOT-323), a 3-pin, surface-mount plastic package with gull-wing leads, footprint compatible with JEDEC MO-203-DA. Thermal performance assumes minimum recommended FR-4 PCB land pattern per datasheet Case 419.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX415 and MPSA42, MSD42SWT1 offers optimal trade-off between SOT-323 miniaturization, 300 V capability, and moderate gain variability-making it preferred for space-constrained, low-to-medium power HV signal paths where thermal budget is tightly controlled.

Availability

MSD42SWT1 is available at Aetrix Electronics and suitable for switched-mode power supply snubbers, low-power relay drivers, and high-voltage signal conditioning requiring stable component supply across industrial automation, consumer electronics, and building control systems.

Supply support for MSD42SWT1 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 (Semiconductor Components Industries, LLC) is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The MSD42SWT1 belongs to onsemi's general-purpose bipolar transistor product line, engineered specifically for cost-sensitive, high-voltage, low-power discrete switching and amplification in compact surface-mount designs.

FAQ

What is the maximum continuous collector current rating for MSD42SWT1?

The MSD42SWT1 has a maximum continuous collector current (IC) rating of 150 mAdc at TA = 25°C. This value decreases with rising ambient temperature due to thermal derating-per the datasheet's SOA curve-and must be applied with appropriate PCB copper area to maintain junction temperature below 150°C. The MSD42SWT1 is not rated for pulsed currents exceeding 200 mAdc without verification of thermal margin.

Does MSD42SWT1 support direct connection to 240 VAC-derived DC rails?

Yes, MSD42SWT1 supports direct connection to 240 VAC-derived DC rails because its V(BR)CEO is rated at 300 Vdc, providing ≥20% margin above peak rectified voltage (≈339 V) only if used with proper transient suppression. In practice, MSD42SWT1 is commonly deployed in auxiliary supplies and snubbers where input is pre-regulated to ≤275 VDC; sustained operation near 300 V requires verified layout and derating per thermal data.

What is the pin configuration of MSD42SWT1 in the SC-70 package?

The MSD42SWT1 uses Style 7 pinout in SC-70 (SOT-323): Pin 1 = Base, Pin 2 = Emitter, Pin 3 = Collector. This matches the mechanical outline in onsemi's Case 419 documentation and is confirmed by the marking diagram and package drawing. Incorrect orientation risks reverse-biasing the emitter-base junction or misapplying collector voltage.

Is MSD42SWT1 suitable for linear amplifier applications?

Yes, MSD42SWT1 is specified for general-purpose amplifier applications per its datasheet title and hFE characterization at IC = 1.0 and 30 mAdc. Its gain range (25–200) and low VCE(sat) support Class-A and Class-AB small-signal stages, but designers must account for thermal drift and ensure VCE remains within safe operating area-especially when driving reactive loads or operating near 150°C junction limit.

How does the RoHS compliance status affect MSD42SWT1's soldering profile?

MSD42SWT1 is Pb-free and RoHS-compliant (marked "G"), requiring a lead-free reflow profile with peak temperature ≥245°C and time above liquidus (TAL) of 60–90 seconds. Its SC-70 package is compatible with standard J-STD-020C Level 1 moisture sensitivity, so baking is not required unless exposed to >60% RH for >168 hours. The MSD42SWT1's thermal characteristics assume this certified process.