STMicroelectronics L78S15CV

Overview

L78S15CV from STMicroelectronics is a three-terminal fixed-output positive linear voltage regulator delivering 15 V at up to 2 A, featuring internal current limiting, thermal shutdown, and safe operating area (SOA) protection. It operates with input voltages up to 30 V (for ≤1 A load), exhibits 150 mV load regulation at 2 A, and maintains output stability without mandatory external capacitance-ideal for local on-card DC-DC regulation in industrial power supplies and embedded control modules.

For engineers reviewing the L78S15CV datasheet, L78S15CV pinout, L78S15CV application, or L78S15CV equivalent, key selection criteria include dropout behavior under thermal stress, quiescent current stability across input voltage range, short-circuit peak current capability (3 A), and TO-220 package thermal resistance (5 °C/W junction-to-case).

Technical Context

The L78S15CV implements a monolithic series pass transistor architecture with built-in foldback current limiting and thermal foldback that reduces output current before junction temperature reaches 150 °C. Its SOA protection prevents secondary breakdown during transient overloads by dynamically constraining I_O × V_CE product.

It functions as a fixed-voltage regulator but supports external configuration for adjustable outputs (e.g., via resistor dividers or tracking circuits), constant-current operation, and remote shutdown-enabling use beyond basic regulation in analog subsystems and power management blocks.

Key Specifications

Pinout & Package

Supplied in TO-220 package (single-gauge variant, 3-pin vertical mount), with metal tab electrically connected to Pin 2 (Ground) and thermally coupled to heatsink interface.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM317T and LD1085V15, the L78S15CV trades adjustability and ultra-low IQ for superior fault resilience (3 A peak SC, SOA, thermal foldback) and proven ruggedness in industrial environments with unpredictable load dynamics.

Availability

L78S15CV is available at Aetrix Electronics and suitable for industrial PLCs, automotive body controllers, test equipment power subsystems, and medical sensor interfaces requiring stable component supply with long-term lifecycle assurance.

Supply support for L78S15CV 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, specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

The L78S series belongs to ST's legacy linear regulator portfolio designed specifically for rugged, cost-effective, fixed-output local regulation in harsh environments-prioritizing fault tolerance and thermal robustness over ultra-low IQ or digital configurability.

FAQ

What is the minimum input voltage required for regulation at full 2 A load?

The L78S15CV requires a minimum input-to-output differential voltage (dropout) of approximately 2.5 V at 2 A and 25 °C, per typical performance curves. Thus, for stable 15 V output at 2 A, VI must be ≥17.5 V. At elevated junction temperatures, dropout increases-designers should verify margin using Figure 8 (Dropout vs. T_J) from the datasheet.

Can L78S15CV be used without an output capacitor?

Yes-the device is internally compensated and stable without an output capacitor. However, adding a 0.1 µF ceramic capacitor at the output significantly improves load transient response, especially in applications with rapidly varying current demand such as motor drivers or digital I/O banks.

Is the metal tab electrically isolated in the TO-220 package?

No-the metal tab of the L78S15CV in TO-220 package is internally connected to Pin 2 (Ground). When mounted to a heatsink, ensure electrical isolation (e.g., mica washer + thermal paste) if the heatsink is not grounded, or use an insulating mounting kit to prevent short circuits.

How does thermal protection behave during sustained overload?

When junction temperature exceeds ~150 °C, thermal shutdown activates, reducing output current to near zero. The device remains latched off until T_J falls below ~135 °C (hysteresis), then resumes regulation automatically-no external reset is needed. This cycle repeats if overload persists, preventing permanent damage.