onsemi LM78M18CT

Overview

LM78M18CT from Fairchild Semiconductor is a three-terminal fixed-output positive voltage regulator delivering 18 V at up to 0.5 A, featuring thermal overload protection, short-circuit protection, and SOA-protected output transistor. It operates across 0°C to +125°C junction temperature and supports input voltages up to 35 V in TO-220 package - commonly used in industrial power supplies and embedded system rails.

For engineers reviewing the LM78M18CT datasheet, pinout, applications, or equivalent options, key selection criteria include dropout voltage (2 V @ 500 mA), load regulation (≤360 mV over 5 mA–0.5 A), ripple rejection (70 dB @ 120 Hz), output voltage drift (−1.1 mV/°C), and thermal resistance (2.5°C/W junction-to-case).

Technical Context

The LM78M18CT implements a classic series-pass linear regulator architecture with internal reference voltage, error amplifier, and current-limited series pass element. Protection circuitry includes dedicated thermal shutdown and safe operating area (SOA) monitoring for the output transistor.

It requires no external components for basic operation but benefits from 0.33 µF input and 0.1 µF output capacitors for stability and transient response. Input voltage must exceed output by ≥2 V (dropout) and remain ≤35 V absolute maximum.

Key Specifications

Pinout & Package

LM78M18CT is housed in a TO-220 package with integral metal tab (pin 2) serving as ground connection and thermal path. The package features standardized 2.54 mm lead pitch and mounting hole for mechanical attachment and heatsinking.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar positive voltage regulator applications.

Compared with LM78M18CT, LM7818CT offers higher current but demands more thermal management, while MC78M18CDT retains identical regulation performance in a surface-mount package - enabling layout flexibility without sacrificing output stability or protection features.

Availability

LM78M18CT is available at Aetrix Electronics and suitable for industrial control systems, test instrumentation, and legacy sensor interface designs requiring stable component supply, long-term obsolescence mitigation, and consistent parametric performance across production batches.

Supply support for LM78M18CT 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 was a U.S.-based semiconductor company specializing in power management, analog, and discrete devices before its acquisition by ON Semiconductor in 2016.

The LM78MXX series was designed as a robust, pin-compatible family of medium-current linear regulators targeting cost-sensitive industrial and embedded applications where reliability and ease of use outweigh switching efficiency requirements.

FAQ

What is the maximum input voltage for LM78M18CT?

The absolute maximum input voltage for LM78M18CT is 35 V. Operation above this level risks permanent damage. For reliable regulation, input must stay within 20.5–33 V per datasheet test conditions - ensuring sufficient headroom above the 18 V output while respecting thermal limits.

Does LM78M18CT require external capacitors?

Yes, LM78M18CT requires a 0.33 µF input capacitor (CI) if located remotely from the bulk filter, and a 0.1 µF output capacitor (CO) is recommended to improve transient response and stability. These values are specified in all electrical test conditions and typical application circuits in the datasheet.

Is LM78M18CT RoHS compliant?

LM78M18CT was manufactured under Fairchild's pre-acquisition RoHS-compliant processes. As a legacy part, it meets exemption 7a (lead in high-melting-temperature solder) for TO-220 packages. Full compliance documentation is available via ON Semiconductor's product change notices and material declarations.

Can LM78M18CT be used in adjustable configurations?

No - LM78M18CT is a fixed-output device. While the LM78MXX family datasheet shows external resistor networks for voltage adjustment (e.g., Figure 3), those methods apply only to the base LM78Mxx part number without suffixes like "CT". LM78M18CT has internal feedback and cannot be reconfigured.

What thermal considerations apply to LM78M18CT in TO-220 package?

LM78M18CT has R_θJC = 2.5°C/W and R_θJA = 66°C/W (TO-220, JEDEC 1S0P board). To avoid thermal shutdown at 0.5 A with 15 V dropout (7.5 W dissipation), a heatsink reducing total thermal resistance to <15°C/W is required - typically achieved with a 15–20 cm² aluminum finned heatsink mounted to the tab via thermal compound.