onsemi MC78M18BTG

Overview

MC78M18BTG from onsemi is a 500 mA, fixed +18 V positive linear voltage regulator in TO-220 package with internal thermal shutdown, short-circuit current limiting, and safe-area compensation. It delivers stable output under varying load (5–500 mA) and input (21–33 V), supporting local on-card regulation in industrial power supplies and automotive subsystems.

For engineers reviewing the MC78M18BTG datasheet, pinout, applications, or equivalent options, key selection criteria include guaranteed ±3% output voltage accuracy over −40°C to +125°C, 2.0 V dropout voltage at 350 mA, 53 dB ripple rejection at 120 Hz, and Pb-free TO-220 packaging with heatsink-connected ground terminal.

Technical Context

The MC78M18BTG implements a monolithic three-terminal series pass regulator architecture with built-in protection circuitry: thermal overload shutdown activates above +150°C junction temperature, short-circuit current limit holds peak output at 350 mA, and safe-area compensation dynamically reduces short-circuit current as input-output differential increases. Its internal design includes 28 active transistors and requires no external components for basic operation.

It operates across an input voltage range of 21–33 V DC to maintain regulated +18 V output, with line regulation ≤10 mV and load regulation ≤30 mV (5–500 mA). Quiescent current remains stable at ≤6.5 mA, and output noise is specified at 100 µV_RMS (10 Hz–100 kHz).

Key Specifications

Pinout & Package

MC78M18BTG uses the TO-220 package (Case 221AB), with the metal tab (heatsink surface) internally connected to Pin 2 (Ground). This configuration simplifies thermal management but requires electrical isolation if mounting to a common chassis.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MC78M18BTG, the MC78M18CDTRKG offers smaller footprint but reduced temperature range, while the NCV78M18BDTRKG provides identical performance with formal automotive qualification - making MC78M18BTG the optimal balance of ruggedness, thermal performance, and cost for non-PPAP industrial use cases.

Availability

MC78M18BTG is available at Aetrix Electronics and suitable for industrial power supplies, automotive body electronics, test equipment, and programmable logic controllers requiring stable component supply and long-term manufacturability.

Supply support for MC78M18BTG 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 for automotive, industrial, cloud, medical, and IoT applications.

The MC78Mxx series is part of onsemi's legacy linear regulator portfolio, designed for robust, drop-in replacement of classic 78xx regulators in cost-sensitive, high-reliability applications demanding thermal resilience and fault protection.

FAQ

What is the output voltage tolerance of the MC78M18BTG over temperature?

The MC78M18BTG guarantees an output voltage of +18 V with ±3% tolerance (17.3–18.7 V) at 25°C, and maintains regulation across its full −40°C to +125°C operating junction temperature range. Output voltage variation over line and load conditions remains within ±0.9 V (17.1–18.9 V) per datasheet specifications.

Can the MC78M18BTG be used without an input bypass capacitor?

The MC78M18BTG can operate without an input bypass capacitor in low-noise, low-impedance source environments, but onsemi strongly recommends a ≥0.33 µF capacitor (tantalum, mylar, or ceramic) placed directly across Pins 1 and 2. This prevents oscillation and ensures stability when connected via long traces or high-impedance sources - a critical design practice for reliable MC78M18BTG deployment.

What is the thermal resistance and maximum power dissipation of the MC78M18BTG in TO-220 package?

In TO-220 (Case 221AB), the MC78M18BTG has θ_JC = 5.0°C/W and θ_JA = 70°C/W (free-air). With infinite heatsinking, maximum power dissipation is internally limited but practically capped at ~7.5 W at 25°C ambient. Derating is required above 25°C - e.g., ~4.5 W at 50°C ambient - per Figure 3 in the datasheet.

Does the MC78M18BTG support adjustable output configurations?

The MC78M18BTG is a fixed +18 V output regulator and does not support direct adjustment. However, it can be used in external configurations - such as with an op-amp error amplifier (Figure 11) or PNP current booster (Figure 12) - to derive higher or variable outputs. These require additional components and careful thermal design, but retain the MC78M18BTG's core regulation and protection features.

Is the MC78M18BTG pin-compatible with other 78Mxx series regulators?

Yes - the MC78M18BTG shares identical TO-220 pinout (Pin 1: Input, Pin 2: Ground, Pin 3: Output) and mechanical footprint with all MC78MxxBTG variants (e.g., MC78M05BTG, MC78M12BTG). This enables direct substitution within the same voltage family when board layout supports the required input voltage range and thermal management.