onsemi MC78M18CTG

Overview

MC78M18CTG from onsemi is a 500 mA, 18 V fixed-output linear voltage regulator in TO-220 package with internal thermal shutdown, short-circuit current limiting, and safe-area compensation for the pass transistor. It delivers stable 18 V output across 5.0 mA–500 mA load current with ±3% output voltage tolerance at 25°C and supports input voltages up to 35 V DC. It is used for local on-card regulation in industrial power supplies and embedded control modules requiring rugged, no-external-components operation.

For engineers reviewing the MC78M18CTG datasheet, pinout, applications, or equivalent options, this page provides verified technical context, key specifications including dropout voltage (2.0 V), ripple rejection (53 dB), load regulation (360 mV), thermal resistance (JC = 5.0 °C/W), and validated alternatives for 18 V fixed-voltage regulation in TO-220 format.

Technical Context

The MC78M18CTG implements a monolithic three-terminal series pass regulator architecture with built-in protection circuitry: thermal overload shutdown activates at +150°C junction temperature, short-circuit current limit holds peak output current to 350 mA under fault, and safe-area compensation dynamically reduces short-circuit current as input-to-output differential increases. Its internal design includes 28 active transistors and operates without external compensation components.

It is specified for 0°C to +125°C operating junction temperature range, requires minimum 21 V input for full 18 V output regulation, and exhibits 100 µV RMS output noise (10 Hz–100 kHz). Ripple rejection remains ≥53 dB at 120 Hz with 22–32 V input and 100 mA load, degrading to 70 dB maximum under optimized conditions.

Key Specifications

Pinout & Package

MC78M18CTG uses the TO-220 package (Case 221AB), with heatsink surface electrically connected to Pin 2 (Ground). The plastic package has thermal resistance θ_JC = 5.0 °C/W and θ_JA = 70 °C/W in free air.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MC78M18CTG, MC7818CT provides higher current capacity at the cost of increased quiescent draw and different thermal behavior, while LM7818CDT delivers tighter regulation and superior ripple suppression but targets broader industrial temperature operation - both require verification of PCB thermal relief and decoupling layout.

Availability

MC78M18CTG is available at Aetrix Electronics and suitable for industrial power supplies, embedded control modules, test equipment power stages, and legacy sensor interfaces requiring stable component supply with long-term lifecycle support.

Supply support for MC78M18CTG 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 manufacturer specializing in energy-efficient power management, analog, and sensing solutions for automotive, industrial, and cloud infrastructure markets.

The MC78Mxx series is designed for rugged, local voltage regulation in space-constrained industrial and embedded systems, offering integrated protection and simplified design with no external components required.

FAQ

What is the maximum input voltage rating for MC78M18CTG?

The MC78M18CTG has an absolute maximum input voltage rating of 35 V DC, as specified in the Maximum Ratings table. Operation above this voltage risks permanent damage. For reliable 18 V output regulation across full load and temperature, input must remain within 21–33 V per electrical characteristics - exceeding 35 V violates device limits regardless of duration or current.

Does MC78M18CTG require input or output capacitors for stable operation?

The MC78M18CTG does not require external capacitors for basic stability, as stated in its "No External Components Required" feature. However, an input bypass capacitor (≥0.33 µF tantalum or ceramic) is recommended when connected via long traces to a noisy or remote power source, and output capacitance may improve transient response. These are design optimizations-not stability prerequisites-for the MC78M18CTG.

What is the thermal resistance and heatsinking requirement for MC78M18CTG at 500 mA?

At 500 mA output and 18 V output, with 24 V input (6 V dropout), power dissipation is ~3 W. With θ_JC = 5.0 °C/W and θ_JA = 70 °C/W in free air, a heatsink reducing θ_JA to ≤25 °C/W is recommended to keep junction temperature below +125°C at +70°C ambient. The TO-220 tab (Pin 2) must be electrically and thermally connected to the heatsink.

Is MC78M18CTG suitable for automotive applications?

The MC78M18CTG is not AEC-Q100 qualified and is rated for 0°C to +125°C junction temperature - it lacks the extended temperature range, qualification testing, and PPAP documentation required for automotive use. For automotive-grade 18 V regulation, consider the NCV78M18BDTRKG (–40°C to +125°C, AEC-Q100 qualified) instead of MC78M18CTG.

How does the short-circuit protection behave in MC78M18CTG?

Under output short-circuit conditions, the MC78M18CTG limits peak output current to approximately 350 mA at 25°C, as confirmed in its Electrical Characteristics table. This current limit decreases with rising junction temperature and input voltage. Protection is automatic and self-resetting: once the fault clears and temperature drops, normal regulation resumes without external intervention - no latch or manual reset is needed for MC78M18CTG.