Send an Inquiry

To receive a quote for your project, please fill in the following information, and we’ll get back to you promptly.

Submit Inventory List

Please fill in the following information, and we’ll get back to you promptly.

Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Voltage Regulators - Linear, Low Drop Out (LDO) Regulators

STMicroelectronics L78S09CV

Name: L78S09CV
Brand: STMicroelectronics
SKU: L78S09CV
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

Compare

Part No.:: L78S09CV

Manufacturer:: STMicroelectronics

Category:: Voltage Regulators - Linear, Low Drop Out (LDO) Regulators

Package:: TO-220-3

Datasheet:: L78S09CV.pdf

Description:: IC REG LINEAR 9V 2A TO220AB

Quantity:: RFQ Add To RFQ list

Payment:

Shipping:

Inventory:3,226

Please send an inquiry. Send us your inquiry, and we will respond immediately.

Product details

Overview

L78S09CV from STMicroelectronics is a three-terminal fixed-output positive voltage regulator IC delivering 9 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 35 V (for 9 V output), maintains ±4% output voltage accuracy over load and temperature, and is commonly used for local on-card regulation in industrial power supplies and embedded control systems.

For engineers reviewing the L78S09CV datasheet, L78S09CV pinout, L78S09CV application, or L78S09CV equivalent, key selection criteria include dropout behavior under 2 A load, thermal resistance (5 °C/W junction-to-case), ripple rejection (47 dB at 120 Hz), and compatibility with TO-220 heatsinking in high-reliability linear power stages.

Technical Context

The L78S09CV implements a monolithic series pass transistor architecture with built-in foldback current limiting and thermal foldback that reduces output current before junction temperature exceeds 150 °C. Its SOA protection prevents destruction during transient overload or short-circuit events without external components.

It functions as a fixed-voltage linear regulator requiring no external feedback network; output voltage is trimmed at wafer level to 9.0 V ±0.35 V (min/max 8.65–9.35 V) at 500 mA and 25 °C. Input-to-output differential voltage must remain ≥2 V for regulation, with typical dropout of ~2.0 V at 2 A load.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Voltage	9.0 V ±0.35 V (8.65–9.35 V) at 500 mA, 25 °C - ensures stable 9 V rail for TTL/CMOS logic and analog subsystems
Max Output Current	2 A continuous - supports high-current loads such as solenoids, motor drivers, or multi-rail converters
Input Voltage Range	12 V to 35 V DC - accommodates unregulated 15–24 V industrial supplies with margin for ripple and transients
Ripple Rejection	47 dB at 120 Hz - suppresses line-frequency noise from transformer-rectifier front-ends
Load Regulation	100 mV (20 mA to 1.5 A), 170 mV (2 A) - maintains tight voltage stability across dynamic load steps
Thermal Resistance	5 °C/W junction-to-case - enables >2 A operation with standard TO-220 heatsink (e.g., 10 °C/W ambient)
Quiescent Current	8 mA - low bias draw preserves efficiency in standby or battery-backed systems
Short-Circuit Current	500 mA (continuous), 3 A peak - limits fault energy while sustaining protection under sustained overload

Pinout & Package

Supplied in TO-220 package with vertical mounting orientation, metal tab electrically connected to Pin 2 (Ground), requiring insulated mounting hardware when heatsink is grounded.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1 (Input)	V_IN	Unregulated DC input; must be ≥2 V above V_OUT for regulation; decoupling capacitor recommended
Pin 2 (Ground)	GND	Common reference for input and output; metal tab is internally bonded to this pin
Pin 3 (Output)	V_OUT	Regulated +9 V output; requires 0.33 µF ceramic bypass capacitor near pin for stability

Key Features

Feature	Design Value
Internal SOA Protection	Prevents second breakdown of series pass transistor during overload or capacitive discharge events
Thermal Shutdown	Activates at T_J ≈ 150 °C and resets automatically upon cooling - eliminates need for external thermal cutoff
Current Limiting	Foldback characteristic reduces short-circuit current to 500 mA, minimizing power dissipation during faults
No External Components Required	Operates as fixed 9 V regulator without resistors or capacitors beyond basic input/output bypassing
High Ripple Rejection	47 dB at 120 Hz enables clean 9 V rail directly from rectified AC without additional filtering stages

Applications

Industrial PLC I/O Power

Automotive Body Control Module

Use Scenario: Powers digital input buffers, relay drivers, and isolated CAN transceivers in programmable logic controller backplanes.

IC Role / Device Role / Timing Role: Local point-of-load regulator converting 24 V bus to stable 9 V for logic-level translation and optocoupler biasing.

Use Value: Eliminates distribution losses and ground bounce from centralized 9 V supply; thermal protection ensures uptime during field wiring faults.

Use Scenario: Supplies 9 V to microcontroller peripherals, window lift motor controllers, and door lock actuators.

IC Role / Device Role / Timing Role: Primary 9 V regulator downstream of automotive alternator rectifier, handling load dump transients via internal SOA protection.

Use Value: Withstands 35 V input surges and delivers 2 A peak for motor startup without external crowbar circuitry.

Test Equipment Power Supply

Legacy Analog Audio Amplifier Bias

Use Scenario: Provides calibrated 9 V rail for op-amp test fixtures, sensor simulators, and calibration standards.

IC Role / Device Role / Timing Role: Precision local regulator ensuring <±0.5% output drift over 0–70 °C for metrology-grade signal conditioning.

Use Value: Low 60 µV RMS output noise and 1 mV/°C tempco enable sub-mV measurement accuracy without post-regulation filtering.

Use Scenario: Generates clean 9 V bias for vintage audio preamp stages using discrete transistors and passive tone controls.

IC Role / Device Role / Timing Role: Low-noise linear regulator replacing aging zener-based shunt supplies in hi-fi equipment service.

Use Value: 47 dB ripple rejection and 17 mΩ output impedance prevent 120 Hz hum injection into sensitive analog gain paths.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
LM7809CT	Same 9 V output, but lower max current (1.5 A), higher dropout (~2.5 V), and no SOA protection	Suitable only for ≤1.5 A loads with ample input headroom; lacks robustness for industrial short-circuit exposure	Select if cost-sensitive and thermal margin allows 1.5 A limit; avoid where 2 A peak or fault resilience is required
LD1085V90	Adjustable version with external resistor divider; 3 A capability; 1.5 V dropout; requires two resistors	Enables fine-tuning (e.g., 9.1 V) and better efficiency at low VIN–VOUT differentials	Choose when adjustable output or lower dropout is needed; adds design complexity vs. drop-in L78S09CV

Compared with LM7809CT, L78S09CV delivers 33% higher current and integrated SOA protection for ruggedized designs; versus LD1085V90, it trades adjustability and lower dropout for simplicity and guaranteed 9.0 V accuracy without external components.

Availability

L78S09CV is available at Aetrix Electronics and suitable for industrial PLC power rails, automotive body control modules, test equipment bias supplies, and legacy audio amplifier refurbishment requiring stable component supply and long-term lifecycle support.

Supply support for L78S09CV 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, power, MCU, and sensor solutions for industrial, automotive, and consumer markets.

The L78S series belongs to ST's legacy linear regulator product line, engineered for robustness in harsh environments-emphasizing fault tolerance, thermal resilience, and ease of use in fixed-voltage applications without external compensation.

FAQ

Is an input capacitor required for stable operation of L78S09CV?

While not strictly required for stability due to internal compensation, a 0.33 µF ceramic capacitor placed within 1 cm of Pin 1 (Input) significantly improves transient response to input voltage spikes and reduces high-frequency noise coupling. ST recommends it for all production designs, especially when the regulator is located more than 10 cm from the main filter capacitor.

Can L78S09CV be used in parallel to increase output current?

No-L78S09CV is not designed for parallel operation. Its output voltage tolerance (±3.9%) and lack of current-sharing features mean mismatched units will cause one device to carry disproportionate load, leading to thermal runaway. For >2 A, use a single higher-current regulator or switch-mode solution instead.

What is the minimum input-to-output voltage differential needed for regulation?

The L78S09CV requires a minimum 2.0 V differential (V_IN – V_OUT) to maintain regulation at full 2 A load, per Figure 8 in the datasheet. At lighter loads (<100 mA), dropout drops to ~1.7 V. Operating below this margin causes output voltage collapse and loss of regulation.

Does L78S09CV require an output capacitor for stability?

No external output capacitor is required for stability-the device is internally compensated-but a 0.1 µF ceramic capacitor at Pin 3 (Output) improves load transient response and reduces output impedance at high frequencies. It is strongly recommended for applications with fast-switching loads like digital I/O or relay coils.

L78S09CV Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-220-3

Packaging:: Tube

Product Status:: Obsolete

Output Configuration:: Positive

Output Type:: Fixed

Number of Regulators:: 1

Voltage - Input (Max):: 35V

Voltage - Output (Min/Fixed):: 9V

Voltage - Output (Max):: -

Voltage Dropout (Max):: -

Current - Output:: 2A

Current - Quiescent (Iq):: 8 mA

Current - Supply (Max):: -

PSRR:: 47dB (120Hz)

Control Features:: -

Protection Features:: Over Current, Over Temperature, Short Circuit

Operating Temperature:: 0°C ~ 150°C

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220

L78S09CV FAQ

1.How can I place an order for L78S09CV through Aetrix?

Please submit a Request for Quotation (RFQ) for L78S09CV on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for L78S09CV reliable?

The price and inventory of L78S09CV are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L78S09CV is usually 5 days.

3.What payment methods are accepted for L78S09CV?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L78S09CV transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L78S09CV?

L78S09CV orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L78S09CV order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for L78S09CV?

For technical support, including L78S09CV datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L78S09CV requirements.

6.How does Aetrix verify that L78S09CV is sourced from the original manufacturer or authorized distributors?

All L78S09CV products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that L78S09CV meets industry standards.

7.What is the process for return or replacement of L78S09CV?

All L78S09CV units undergo pre-shipment inspection (PSI). If there is an issue with L78S09CV, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The L78S09CV part is unused and in its original packaging.

Return procedure for L78S09CV:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

Tech Hub

2026-09-07 TTL vs CMOS Logic Levels: 74HC and 74HCT Compatibility Explained

TTL and CMOS logic families differ in thresholds, loading, output drive, power and timing. This engineering guide compares 74HC and 74HCT, calculates noise margins and checks 3.3 V/5 V compatibility.

2026-09-04 Logic Level Shifter: How to Connect 3.3V and 5V Logic Safely

A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.

2026-09-03 74HC595 vs TPIC6B595: Output Drive, Pinout, Current, and Load Selection

The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…

2026-09-02 74HC595 Pinout, Timing, Output Current, and Applications

The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…

2026-09-01 Latch vs Flip-Flop: Timing, Differences and Design Choices

A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…

2026-08-30 D Latch Circuit: Truth Table, Timing, ICs and Applications

A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …

2026-08-28 SR Latch Explained: NOR and NAND Circuits, Truth Tables, and Applications

An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…

2026-08-27 Latch Circuit: SR and D Latches, Truth Tables, Timing, and Applications

Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…

2026-08-21 What Is an LED Driver? Types, Circuits, Dimming, and Selection

An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…

2026-08-18 Operational Amplifier (Op Amp): Basics, Configurations, Feedback and Applications

Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…