STMicroelectronics L78L24ACUTR

Overview

L78L24ACUTR from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 24 V output at up to 100 mA, featuring internal current limiting, thermal shutdown, and short-circuit protection. It requires no external components, supports input voltages up to 40 V, and maintains ±4% output tolerance over 0–125 °C junction temperature for industrial power rail regulation.

For engineers reviewing the L78L24ACUTR datasheet, L78L24ACUTR pinout, L78L24ACUTR application, or L78L24ACUTR equivalent, this device serves as a drop-in replacement for Zener/resistor regulators in low-noise local supply domains-especially where quiescent current (6.5 mA typ.), dropout voltage (1.7 V), and ripple rejection (31–37 dB at 120 Hz) are critical selection criteria.

Technical Context

The L78L24ACUTR implements a monolithic silicon-based series pass architecture with built-in thermal overload and short-circuit foldback protection. Its regulation loop stabilizes output against line variations (≤300 mV line regulation) and load changes (≤100 mV load regulation over 1–40 mA) without external compensation.

It operates across an input range of 27–38 V for nominal 24 V output, sustaining full 100 mA delivery only with adequate PCB copper heat-sinking due to its TO-92 package's 200 °C/W junction-to-ambient thermal resistance-making it suitable for low-power auxiliary rails rather than high-current primary supplies.

Key Specifications

Pinout & Package

Supplied in TO-92 package (JEDEC TO-226AA), with 3 leads: Input (Pin 1), Ground (Pin 2), Output (Pin 3). Pin numbering follows standard top-view orientation per DS0424 Rev 30 Figure 2.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM78L24ACZ/NOPB and MC78L24ACP, the L78L24ACUTR provides superior supply ripple rejection, tighter output tolerance, and guaranteed operation across the full industrial temperature range - making it the preferred choice for mission-critical embedded power rails.

Availability

L78L24ACUTR is available at Aetrix Electronics and suitable for industrial sensor interfaces, PLC I/O modules, medical diagnostic equipment, and building automation controllers requiring stable component supply with consistent parametric performance and long-term manufacturability.

Supply support for L78L24ACUTR 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 microcontrollers, power management ICs, and analog devices for industrial, automotive, and consumer markets.

The L78L series belongs to ST's legacy linear regulator product line, engineered specifically for cost-sensitive, low-power local regulation tasks where simplicity, reliability, and thermal robustness outweigh high-efficiency switching requirements.

FAQ

What is the minimum input voltage required for stable 24 V output?

The L78L24ACUTR requires a minimum input voltage of 25.7 V to maintain regulation under worst-case conditions (24 V −4% = 22.8 V output + 1.7 V dropout + margin). At 27 V input, it delivers full 24 V output across 1–40 mA load and 0–125 °C junction temperature per Table 21.

Can this regulator be used in parallel to increase output current?

No - the L78L24ACUTR lacks current-sharing capability and has no built-in balancing features. Paralleling units risks thermal runaway due to mismatched dropout voltages and load distribution. For >100 mA, use a single higher-current regulator or add an external pass transistor per Figure 14 in DS0424.

Is a heat sink required for continuous 100 mA operation?

Yes - in TO-92 packaging, continuous 100 mA at 24 V output with 33 V input yields ~0.9 W dissipation. With R_thJA = 200 °C/W, junction temperature rises ~180 °C above ambient - exceeding the 125 °C limit. A minimum 6 cm² copper pour is mandatory per Table 2 footnote 1 to sustain rated current.

Does the L78L24ACUTR support reverse-polarity input protection?

No - the device contains no internal reverse-voltage blocking diode. Applying reversed input voltage will forward-bias internal substrate junctions, causing latch-up or permanent damage. An external series Schottky diode (e.g., 1N5817) is required if reverse polarity exposure is possible in the application.