STMicroelectronics L7908ACV

Overview

L7908ACV from STMicroelectronics is a fixed-output, three-terminal negative linear voltage regulator delivering -8 V at up to 1.5 A, featuring thermal overload protection, short-circuit current limiting, and output transition SOA protection. It operates with input voltages down to -35 V (for -8 V output), supports local on-card regulation in split-supply systems, and is commonly used in industrial power supplies and analog signal conditioning circuits requiring stable negative rail generation.

For engineers reviewing the L7908ACV datasheet, L7908ACV pinout, L7908ACV application, or L7908ACV equivalent, key selection considerations include dropout voltage (1.1 V @ 1 A), load regulation (±80 mV over 250–750 mA), output voltage accuracy (±2% at 25 °C), thermal resistance (R_thJA = 50 °C/W in TO-220), and compatibility with standard ±15 V dual-rail designs.

Technical Context

The L7908ACV implements a monolithic PNP pass transistor architecture with internal current limiting, thermal shutdown, and safe operating area (SOA) protection for sustained negative output delivery. Its feedback loop maintains regulated -8 V output across line variations (-11.5 V to -23 V input) and load changes (5 mA to 1.5 A), with pulse-tested load/line regulation specified at constant junction temperature.

Designed for fixed-voltage operation, it accepts external components to enable adjustable output configurations-e.g., using resistive dividers for higher negative outputs or parallel devices for increased current. It requires minimum 2.2 µF input and 1 µF output capacitors (solid tantalum recommended) for stability and transient response per ST's test circuit conditions.

Key Specifications

Pinout & Package

L7908ACV is supplied in TO-220 package (3-pin, vertical mounting, metal tab connected to GND). The case serves as thermal path and electrical ground reference; mounting screw must be isolated unless GND connection is intentional.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar negative fixed-voltage regulation applications.

Compared with LM337T and MC7908CT, L7908ACV offers tighter output tolerance, lower dropout, and superior thermal performance-making it optimal for space-constrained industrial and test equipment where reliability and precision are prioritized over adjustability or lowest unit cost.

Availability

L7908ACV is available at Aetrix Electronics and suitable for industrial power supplies, analog signal conditioning circuits, test & measurement equipment, and legacy controller upgrades requiring stable component supply and long-term obsolescence management.

Supply support for L7908ACV 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, analog chips, and discrete devices for industrial, automotive, and consumer markets.

L7908ACV belongs to the L79xxAC series of three-terminal negative linear regulators-engineered specifically for robust local regulation in split-supply systems, with emphasis on thermal resilience, fault protection, and compatibility with legacy L78xxA positive counterparts.

FAQ

What is the minimum input voltage required for L7908ACV to maintain regulation?

The L7908ACV requires a minimum input voltage of -9.1 V (i.e., at least 1.1 V more negative than the -8 V output) to sustain regulation at 1 A load and 25 °C junction temperature. At lighter loads or lower temperatures, input as low as -8.5 V may suffice-but design margins should account for worst-case dropout (1.4 V) and temperature drift.

Can L7908ACV be used in parallel for higher current capability?

Yes, but only with external ballast resistors (typically 0.1 Ω, 1% tolerance) in series with each output to ensure current sharing. Without balancing, mismatched dropout voltages cause one device to dominate conduction-risking thermal runaway. ST does not recommend direct paralleling without resistor compensation.

Is a heat sink mandatory for L7908ACV in TO-220 package?

A heat sink is required for continuous operation above ~500 mA at ambient temperatures exceeding 50 °C. With R_thJA = 50 °C/W, 1 A load dissipating 1.1 W generates ~55 °C rise-exceeding the 125 °C max junction limit if ambient is >70 °C. For reliable 1.5 A operation, a heatsink reducing R_thJA to ≤20 °C/W is recommended.

Does L7908ACV require input and output capacitors, and what types are recommended?

Yes: minimum 2.2 µF input and 1 µF output capacitors are mandatory for stability. ST specifies solid tantalum for both; if aluminum electrolytic is used, values must be increased tenfold (≥22 µF input, ≥10 µF output) due to higher ESR. Input capacitor placement must be within 2 cm of the IN pin to suppress high-frequency noise.