STMicroelectronics L78M15CDT-TR

Overview

L78M15CDT-TR from STMicroelectronics is a three-terminal positive fixed-voltage linear regulator delivering 15 V ±4 % output at up to 500 mA, featuring thermal overload protection, short-circuit current limiting, and safe operating area (SOA) protection. It operates with input voltages up to 35 V and is used for local on-card regulation in industrial power supplies, embedded control modules, and sensor interface circuits.

For engineers reviewing the L78M15CDT-TR datasheet, L78M15CDT-TR pinout, L78M15CDT-TR application, or L78M15CDT-TR equivalent, key selection criteria include output voltage tolerance (±4 %), junction temperature range (0 to 150 °C), dropout voltage (2 V), supply voltage rejection (54 dB at 120 Hz), and TO-220FP package thermal resistance (R_thJC = 5 °C/W).

Technical Context

This device implements a monolithic series pass transistor with internal current limiting, thermal shutdown, and SOA compensation-ensuring robustness under sustained overload or fault conditions. Its architecture requires no external components for basic operation but supports adjustable output configurations using external resistors or transistors.

The regulator maintains stable 15 V output across load currents from 5 mA to 500 mA and input-output differentials from 2 V to 20 V, with line regulation of ≤50 mV (VI = 20–30 V) and load regulation of ≤150 mV (IO = 5–200 mA) at TJ = 25 °C.

Key Specifications

Pinout & Package

Supplied in TO-220FP (IPAK) package: insulated case, vertical mounting, 3-pin single-gauge outline with metal tab (pin 2) acting as both output and thermal path. Requires heatsink for >250 mA continuous operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with L78M15CDT-TR, the AB-grade variant improves voltage accuracy and low-temperature operation at higher cost, while the MC78M15CDTG offers identical electrical specs in a non-insulated TO-220-making it viable only where electrical isolation is unnecessary and board layout permits direct tab grounding.

Availability

L78M15CDT-TR is available at Aetrix Electronics and suitable for industrial automation systems, medical instrumentation, and test equipment requiring stable component supply with guaranteed long-term availability and full traceability.

Supply support for L78M15CDT-TR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The L78M series belongs to ST's precision 500 mA linear regulator product line, engineered for cost-effective, robust local regulation in space-constrained and thermally demanding applications where simplicity and reliability are prioritized over ultra-low quiescent current or switching efficiency.

FAQ

What is the maximum input voltage for L78M15CDT-TR?

The absolute maximum DC input voltage is 35 V for output voltages between 5 V and 18 V. Since L78M15CDT-TR delivers 15 V, it supports up to 35 V input. Exceeding this risks permanent damage-even briefly-due to internal junction breakdown. For reliable operation, keep VI ≤ 30 V under full load to maintain adequate power dissipation margin.

Does L78M15CDT-TR require input and output capacitors?

Yes-an input capacitor (≥0.33 µF tantalum or ceramic) is required if the regulator is located more than ~2 cm from the bulk filter capacitor, to suppress high-frequency instability. An output capacitor (≥0.1 µF) is not mandatory for stability but improves transient response and reduces output impedance. Both must be placed with minimal lead length to avoid parasitic inductance.

How does thermal protection work in L78M15CDT-TR?

Thermal protection activates when junction temperature reaches approximately 150 °C, disabling the pass transistor until temperature falls below ~135 °C. This is achieved via an on-die thermal sensor and shutdown circuit-not a simple trip-and-hold latch-allowing automatic recovery once cooled. The TO-220FP package's R_thJC = 5 °C/W enables effective heatsinking to sustain 500 mA continuously below 60 °C ambient.

Can L78M15CDT-TR be used to generate adjustable output voltages?

Yes-though designed as a fixed 15 V regulator, it can serve as the core of adjustable configurations. Examples include adding a resistor divider to raise output voltage (VO = 15 V × (1 + R2/R1)), using an external transistor to boost current, or configuring constant-current sinks. All such circuits retain the device's internal protections but require careful stability analysis per Figure 19–22 in DS0425.