onsemi MMBTA42

Overview

MMBTA42 from Fairchild Semiconductor is an NPN high-voltage amplifier transistor designed for video output stages in color CRT displays and other high-voltage switching or amplification applications. It features a 300 V collector-emitter breakdown voltage (V_(BR)CEO), 500 mA continuous collector current (I_C), and 625 mW power dissipation at 25°C in the SOT-23 package. Its DC current gain (h_FE) reaches 40 at I_C = 10 mA and V_CE = 10 V.

For engineers reviewing the MMBTA42 datasheet, pinout, applications, or equivalent options, key selection criteria include high-voltage capability (300 V), low saturation voltage (V_CE(sat) = 0.5 V @ I_C = 20 mA), thermal resistance (R_θJA = 357 °C/W), and compatibility with compact SOT-23 PCB layouts in CRT flyback, HV bias, and pulse amplifier circuits.

Technical Context

The MMBTA42 is fabricated using Fairchild's Process 48, optimized for high-voltage NPN operation. Its structure supports stable gain and low leakage (I_CBO ≤ 0.1 µA @ V_CB = 200 V) across –55°C to +150°C junction temperature range. The device exhibits a current gain–bandwidth product (f_T) of 50 MHz at I_C = 10 mA and V_CE = 20 V, enabling use in medium-frequency amplification.

It delivers low collector-base capacitance (C_cb = 3.0 pF @ V_CB = 20 V), supporting fast switching transitions. Base-emitter saturation voltage is specified at 0.9 V (I_C = 20 mA, I_B = 2.0 mA), ensuring predictable drive requirements in linear and saturated-mode designs.

Key Specifications

Pinout & Package

SOT-23 surface-mount package (FS PKG Code 49), marked "1D", with lead-free finish and RoHS-compliant construction. Thermal pad not present; mounting per JEDEC MO-178 standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA42, MMBTA42 offers space savings and automated assembly compatibility but requires tighter thermal management due to higher R_θJA; compared with PN2222A, MMBTA42 provides essential 300 V capability absent in the latter, making it non-interchangeable in HV designs.

Availability

MMBTA42 is available at Aetrix Electronics and suitable for color CRT video output stages, high-voltage bias generators, pulse amplifiers for HV sensors, and legacy industrial relay drivers requiring stable component supply and long-lifecycle support.

Supply support for MMBTA42 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

Fairchild Semiconductor (now part of ON Semiconductor) is a U.S.-based semiconductor manufacturer specializing in power management, analog, and discrete devices for industrial, automotive, and consumer systems.

The MMBTA42 belongs to Fairchild's high-voltage bipolar transistor product line, engineered specifically for CRT video output, HV pulse amplification, and legacy industrial control applications demanding rugged 300 V operation.

FAQ

What is the maximum collector-emitter voltage rating for the MMBTA42?

The MMBTA42 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 is validated per Absolute Maximum Ratings and Electrical Characteristics tables in the official Fairchild datasheet. Operation beyond 300 V risks irreversible avalanche failure. The MMBTA42 must be used with appropriate voltage derating and snubber networks in real-world HV circuits.

Is the MMBTA42 pin-compatible with the MPSA42?

No - the MMBTA42 uses a SOT-23 surface-mount package with emitter-base-collector pinout (1-2-3), while the MPSA42 uses a TO-92 through-hole package with collector-base-emitter pinout (1-2-3). Their physical pin assignments and footprints are incompatible. Board redesign is required to substitute MMBTA42 for MPSA42 or vice versa; they share identical electrical specifications but differ in package, thermal performance, and mounting method.

What is the typical DC current gain (h_FE) of the MMBTA42 at 10 mA collector current?

The MMBTA42 exhibits a minimum h_FE of 40 at I_C = 10 mA and V_CE = 10 V, per the Small Signal Characteristics table. Typical values range from 60 to 100 under those conditions, as confirmed by the "DC Current Gain vs Collector Current" graph. This gain supports stable biasing in linear video amplifier stages and ensures predictable base drive requirements in switching applications.

Can the MMBTA42 be used in switching power supplies?

Yes - the MMBTA42 is suitable for low-to-medium frequency switching power supplies operating below 100 kHz, particularly in flyback or boost converter primary-side switch roles where 300 V blocking and 500 mA current handling are required. Its 50 MHz f_T, 3.0 pF C_cb, and 0.5 V V_CE(sat) support efficient switching, but thermal design must account for R_θJA = 357 °C/W in SOT-23. It is not recommended for >200 kHz SMPS due to limited f_T and SOA constraints.

Does the MMBTA42 have a built-in thermal pad or exposed collector tab?

No - the MMBTA42 in SOT-23 package (FS PKG Code 49) has no thermal pad or exposed metal tab. The collector terminal connects solely via Pin 3 (leadframe), and heat dissipation relies entirely on PCB copper area and trace conduction. Fairchild specifies R_θJA = 357 °C/W for a standard FR-4 board (1.6" × 1.6" × 0.06"); adding thermal vias under the collector pad significantly improves performance. The MMBTA42 is not a thermally enhanced variant like SOT-223-packaged alternatives.