STMicroelectronics L78L09ACZ

Overview

L78L09ACZ from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 9 V output at up to 100 mA, featuring internal current limiting, thermal overload protection, and short-circuit protection. It requires no external components and is rated for ±4% output voltage tolerance (A grade) in TO-92 package, commonly used for local on-card regulation in microcontroller power rails and sensor interface circuits.

For engineers reviewing the L78L09ACZ datasheet, L78L09ACZ pinout, L78L09ACZ application, or L78L09ACZ equivalent, key selection criteria include dropout voltage (1.7 V), quiescent current (6 mA at 25 °C), output noise (70 µV RMS, 10 Hz–100 kHz), and supply voltage rejection (37–44 dB at 120 Hz), all critical for low-noise analog subsystems and battery-powered embedded designs.

Technical Context

The L78L09ACZ employs monolithic bipolar technology with built-in thermal shutdown and foldback current limiting, enabling robust operation without external protection circuitry. Its fixed-output architecture eliminates trimming components while maintaining stability with only 0.33 µF input and 0.1 µF output capacitors.

Designed for local regulation, it operates across an input voltage range of 11.5 V to 23 V (min/max for 9 V output), supports junction temperatures from 0 °C to 125 °C, and achieves 1.7 V dropout-enabling use with marginal input margins in industrial control and automotive body electronics.

Key Specifications

Pinout & Package

Supplied in TO-92 package (JEDEC TO-226AA), with molded plastic case, axial leads, and standard through-hole mounting. Thermal resistance is 200 °C/W (junction-to-ambient, no heatsink); derating required above 60 °C ambient.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM78L09ACZ and MC78L09ACP, the L78L09ACZ offers superior supply rejection and guaranteed low-noise performance across temperature, making it optimal for mixed-signal systems where analog accuracy cannot be compromised by power rail artifacts.

Availability

L78L09ACZ is available at Aetrix Electronics and suitable for industrial sensor interfaces, automotive body electronics, and embedded microcontroller core supplies requiring stable component supply with long-term lifecycle assurance.

Supply support for L78L09ACZ 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 silicon solutions for automotive, industrial, and consumer markets since 1987.

The L78L series was developed as a cost-optimized, drop-in replacement for discrete Zener/resistor regulators in space-constrained applications, emphasizing reliability, ease of use, and compatibility with legacy through-hole assembly processes.

FAQ

What is the minimum input voltage required for stable 9 V output from the L78L09ACZ?

The L78L09ACZ requires a minimum input voltage of 11.5 V to maintain regulation at full 100 mA load and 25 °C ambient, based on its 1.7 V dropout specification. At higher temperatures or lighter loads, operation down to 10.7 V may be possible, but design margin should retain ≥11.5 V to guarantee compliance across process, voltage, and temperature (PVT) corners.

Can the L78L09ACZ be used in parallel to increase output current?

No-parallel operation is not recommended due to mismatch in output voltage (±4% tolerance) and lack of current-sharing circuitry, which would cause one device to dominate conduction and overheat. For >100 mA, use a single higher-current regulator (e.g., L7809CP) or add an external pass transistor with proper biasing and thermal feedback.

Does the L78L09ACZ require input and output capacitors, and what values are mandatory?

Yes: a 0.33 µF ceramic capacitor is required on VIN and a 0.1 µF ceramic capacitor on VOUT, placed as close as possible to the respective pins. These values are specified in the datasheet for stability across all operating conditions; substituting with larger electrolytics or omitting either capacitor risks oscillation or poor transient response.

How does the L78L09ACZ's thermal protection behave during continuous overload?

Under sustained overload, the L78L09ACZ enters thermal shutdown when junction temperature exceeds ~165 °C, cutting output until die temperature falls below ~145 °C, then automatically resuming regulation. This cycle repeats without latch-up, protecting the device-but repeated cycling degrades long-term reliability, so proper heatsinking or current limiting must be implemented in the system design.