onsemi MC78M08BTG

Overview

MC78M08BTG from onsemi is a 500 mA, fixed +8.0 V positive voltage regulator in TO-220 package, featuring internal thermal shutdown, short-circuit current limiting, and safe-area compensation for rugged local on-card regulation. It delivers stable output under load currents up to 500 mA with ≤8.30 V variation over line/load/temperature, 2.0 V dropout, and 56 dB ripple rejection at 100 mA - ideal for industrial power supplies and embedded control modules.

For engineers reviewing the MC78M08BTG datasheet, pinout, applications, or equivalent options, key selection criteria include its −40°C to +125°C operating junction range, Pb-free TO-220 package with heatsink-connected ground pin, ±2% output accuracy (MC78M08AB variant), and compatibility with standard linear regulator design practices including input bypassing and thermal management.

Technical Context

The MC78M08BTG implements a monolithic three-terminal series pass architecture with built-in protection circuitry: thermal overload shutdown triggers at ~150°C junction temperature, short-circuit current limit holds peak output at ~350 mA, and safe-area compensation dynamically reduces short-circuit current as pass transistor V_CE increases. Its internal bias network draws 3.2–6.0 mA quiescent current and maintains ±0.2 mV/°C average temperature coefficient.

Designed for fixed-output operation without external components, it requires only input and output capacitors for stability - typically 0.33 µF tantalum at input and 0.1 µF ceramic at output. Ripple rejection degrades above 1 kHz but remains ≥56 dB at 120 Hz across 11.5–21.5 V input range, supporting noisy DC bus conditioning in motor drives and automotive subsystems.

Key Specifications

Pinout & Package

MC78M08BTG uses the industry-standard TO-220 package (Case 221AB) with three leads and an exposed metal tab thermally/electrically tied to Pin 2 (Ground). The heatsink surface must be isolated from other potentials unless intentionally grounded.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-output linear regulator applications.

Compared with MC78M08CDTRKG and NCV78M08BDTRKG, the MC78M08BTG offers through-hole TO-220 mounting with direct heatsink attachment - simplifying thermal design in industrial enclosures where airflow and mechanical robustness outweigh SMT density advantages.

Availability

MC78M08BTG is available at Aetrix Electronics and suitable for industrial control systems, automotive body electronics, and medical instrumentation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MC78M08BTG 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 silicon solutions for automotive, industrial, cloud, medical, and IoT applications.

The MC78M00 series was designed as a rugged, drop-in upgrade to legacy 78xx regulators - delivering 500 mA output with enhanced thermal protection and automotive-grade reliability in both through-hole and surface-mount packages.

FAQ

What is the maximum input voltage rating for MC78M08BTG?

The MC78M08BTG has an absolute maximum input voltage of 40 Vdc under transient conditions, though continuous operation is limited to 35 Vdc per the datasheet's Maximum Ratings table. For reliable 8 V output, the recommended input range is 10.5 V to 25 V - ensuring sufficient headroom for dropout while avoiding excessive power dissipation.

Does MC78M08BTG require external capacitors for stable operation?

Yes, MC78M08BTG requires an input bypass capacitor (≥0.33 µF tantalum or low-ESR ceramic) placed close to Pin 1, and an output capacitor (≥0.1 µF ceramic) at Pin 3. These stabilize the control loop and suppress high-frequency noise; omitting them risks oscillation or poor transient response, especially with long input traces or large load capacitance.

How does the thermal shutdown feature work in MC78M08BTG?

The MC78M08BTG integrates a thermal sensing circuit that disables the pass transistor when junction temperature reaches approximately +150°C. This shutdown is non-latching - the device automatically resumes regulation once cooled below the hysteresis threshold (~130°C). It protects against sustained overload, insufficient heatsinking, or ambient temperature excursions without external intervention.

Can MC78M08BTG be used in automotive applications?

Yes, MC78M08BTG is rated for −40°C to +125°C operating junction temperature and features internal protections suitable for automotive environments. While not AEC-Q100 certified itself, it shares identical electrical specs with the NCV78M08BDTRKG - the automotive-qualified variant - making it appropriate for non-safety-critical vehicle subsystems like infotainment power rails or lighting controls.

What is the typical dropout voltage of MC78M08BTG at full load?

The MC78M08BTG exhibits a typical dropout voltage of 2.0 Vdc at TJ = 25°C and IO = 350 mA. At its maximum rated 500 mA output, dropout remains ≤2.0 V under most conditions - meaning a minimum input of 10 V is required to sustain 8 V output. This value increases slightly at elevated temperatures or extreme load edges.