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

STMicroelectronics L78S18CV

Name: L78S18CV
Brand: STMicroelectronics
SKU: L78S18CV
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: L78S18CV

Manufacturer:: STMicroelectronics

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

Package:: TO-220-3

Datasheet:: L78S18CV.pdf

Description:: IC REG LINEAR 18V 2A TO220AB

Quantity:: RFQ Add To RFQ list

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Inventory:3,725

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Product details

Overview

L78S18CV from STMicroelectronics is a three-terminal positive linear voltage regulator IC delivering a fixed 18 V output with up to 2 A continuous current, thermal shutdown, short-circuit protection, and safe operating area (SOA) protection. It operates with a minimum input voltage of 20.5 V (for 1 A load), exhibits 180 mV line regulation (22–28 V input range), and maintains 22 mΩ typical output resistance - used in industrial power supplies, local board-level regulation, and embedded system auxiliary rails.

For engineers reviewing the L78S18CV datasheet, L78S18CV pinout, L78S18CV application, or L78S18CV equivalent, key selection criteria include dropout margin at 2 A, thermal resistance (5 °C/W junction-to-case), output noise (110 µV RMS, 10 Hz–100 kHz), and compatibility with TO-220 heatsink mounting for sustained high-current operation.

Technical Context

The L78S18CV implements a monolithic series pass transistor architecture with internal current limiting, thermal foldback, and SOA protection circuitry - eliminating external protection components. Its feedback loop is internally compensated for stability without an output capacitor, though one improves transient response.

It functions as a fixed-output linear regulator requiring no external resistors; however, application circuits in the datasheet confirm support for adjustable configurations (e.g., higher output voltages via external resistive divider or current boosting with external transistors), while maintaining core protection features across all modes.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Voltage	18 V ±5% (17.1–18.9 V) - tightly regulated fixed rail for 18 V logic or analog subsystems.
Max Output Current	2 A continuous - supports high-power peripherals without external current boost under adequate heatsinking.
Input Voltage Range	20.5 V to 30 V (for 1 A); 22–28 V specified for 180 mV line regulation - defines minimum headroom and max safe DC input.
Dropped Voltage (Dropout)	Typ. 2.5 V at 2 A - determines minimum input–output differential required to sustain regulation.
Output Resistance	22 mΩ at 1 kHz - directly impacts load regulation error and AC ripple rejection performance.
Supply Voltage Rejection	43 dB at 120 Hz - quantifies attenuation of low-frequency input ripple (e.g., rectified AC) on output.
Thermal Resistance (Junction–Case)	5 °C/W - enables precise junction temperature estimation when mounted to heatsink with known thermal interface.

Pinout & Package

Supplied in TO-220 package with standard 3-pin vertical mounting configuration (heat tab electrically connected to ground pin). Requires mechanical mounting to heatsink for >1 A operation.

Pin/Terminal	Circuit Role	Design Meaning
1 (Input)	V_IN	Unregulated DC input supply - must exceed output by ≥2.5 V at full load; connects to bulk capacitance.
2 (Ground)	GND / Case	Reference node and thermal path - electrically tied to metal tab; must be low-impedance connection to PCB ground plane.
3 (Output)	V_OUT	Regulated 18 V output - feeds downstream circuitry; optional 0.33 µF ceramic capacitor recommended for high-frequency stability.

Key Features

Feature	Design Value
Internal Short-Circuit Protection	Limits output current to ≤500 mA during fault - prevents damage during wiring errors or load shorts.
Thermal Shutdown	Activates at ~150 °C junction temperature - automatically disables output until safe temperature is restored.
Safe Operating Area (SOA) Protection	Prevents second breakdown of internal pass transistor - ensures reliability under simultaneous high voltage/current stress.
No External Compensation Required	Internally compensated for stability with or without output capacitor - simplifies layout and reduces BOM count.
Low Quiescent Current	8 mA typical - minimizes standby power loss in always-on systems.

Applications

Industrial Power Supply

Embedded System Auxiliary Rail

Use Scenario: Local regulation of 18 V for PLC I/O modules powered from a shared 24 V bus.

IC Role / Device Role / Timing Role: Primary fixed-voltage regulator providing clean, protected 18 V rail independent of upstream distribution losses.

Use Value: Eliminates need for point-of-load DC/DC converters; thermal and short-circuit protection ensures uptime in harsh factory environments.

Use Scenario: Powering analog front-end circuitry (op-amps, ADC references) in a medical sensor node.

IC Role / Device Role / Timing Role: Low-noise (110 µV RMS), stable 18 V source for precision signal conditioning stages.

Use Value: Maintains SNR integrity without requiring additional filtering; SOA protection guards against transient overloads during sensor calibration.

Test Equipment Bias Supply

Legacy Industrial Controller

Use Scenario: Generating 18 V bias for RF power amplifier stages in benchtop signal generators.

IC Role / Device Role / Timing Role: High-current (2 A capable), low-impedance voltage source supporting dynamic load steps.

Use Value: Output resistance of 22 mΩ ensures <100 mV droop during 1 A load transients - critical for amplifier linearity verification.

Use Scenario: Replacing aging 7818 regulators in field-deployed CNC motion controllers.

IC Role / Device Role / Timing Role: Pin-compatible upgrade offering enhanced thermal robustness and SOA protection over legacy parts.

Use Value: Extends service life in convection-cooled enclosures where ambient temperatures exceed 70 °C.

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
LM7818CT	Higher dropout (2.8 V typ. at 2 A), lower SVR (40 dB), no SOA protection - older bipolar design.	Less tolerant of low-headroom inputs; requires external SOA protection for high-stress loads.	Choose only if footprint compatibility is mandatory and thermal margin exceeds 10 °C.
LD1085V18	Lower quiescent current (5 mA), adjustable version available, but max current limited to 1.5 A.	Suitable for lower-power 18 V rails where efficiency and thermal footprint are prioritized over peak current.	Select when load never exceeds 1.5 A and board space allows SOT-223 or DPAK alternatives.

Compared with LM7818CT, L78S18CV delivers superior thermal resilience and built-in SOA protection; versus LD1085V18, it trades higher quiescent current for 33% more output current and ruggedized fault handling - making it optimal for industrial 2 A fixed-rail applications.

Availability

L78S18CV is available at Aetrix Electronics and suitable for industrial power supplies, embedded system auxiliary rails, test equipment bias supplies, and legacy industrial controller replacements requiring stable component supply and long-term manufacturability.

Supply support for L78S18CV 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, specializing in automotive, industrial, and power management ICs with strong emphasis on reliability and longevity.

The L78S series belongs to ST's legacy linear regulator product line, designed specifically for robust, cost-effective fixed-voltage regulation in industrial control, instrumentation, and power conversion systems where simplicity and fault tolerance are critical.

FAQ

What is the minimum input voltage required for L78S18CV to regulate at full 2 A?

The datasheet specifies a minimum input voltage of 20.5 V for 1 A operation. At 2 A, dropout voltage rises to ~2.5 V; thus, minimum input is 20.5 V. For reliable 2 A regulation across temperature, 21.5 V is recommended to maintain margin above worst-case dropout.

Can L78S18CV be used without an output capacitor?

Yes - the device is internally compensated and stable without an output capacitor. However, a 0.33 µF ceramic capacitor is recommended at the output to improve transient response and suppress high-frequency noise, especially when the regulator is remote from the load.

Is the metal tab on the TO-220 package electrically connected?

Yes - the metal tab is internally connected to Pin 2 (Ground). This provides both thermal conduction and electrical grounding. When mounting to a heatsink, ensure electrical isolation (e.g., mica washer + thermal paste) unless the heatsink is grounded.

Does L78S18CV support adjustable output voltages?

Not natively - it is a fixed 18 V device. However, the datasheet provides application circuits (e.g., Figure 19 and Figure 20) showing how external resistors and transistors can configure it for higher or adjustable outputs, retaining internal protection features in those configurations.

L78S18CV 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):: 18V

Voltage - Output (Max):: -

Voltage Dropout (Max):: -

Current - Output:: 2A

Current - Quiescent (Iq):: 8 mA

Current - Supply (Max):: -

PSRR:: 43dB (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

L78S18CV FAQ

1.How can I place an order for L78S18CV through Aetrix?

Please submit a Request for Quotation (RFQ) for L78S18CV 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 L78S18CV reliable?

The price and inventory of L78S18CV are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L78S18CV is usually 5 days.

3.What payment methods are accepted for L78S18CV?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L78S18CV transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L78S18CV?

L78S18CV orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L78S18CV 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 L78S18CV?

For technical support, including L78S18CV datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L78S18CV requirements.

6.How does Aetrix verify that L78S18CV is sourced from the original manufacturer or authorized distributors?

All L78S18CV 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 L78S18CV meets industry standards.

7.What is the process for return or replacement of L78S18CV?

All L78S18CV units undergo pre-shipment inspection (PSI). If there is an issue with L78S18CV, 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 L78S18CV part is unused and in its original packaging.

Return procedure for L78S18CV:

1.Submit a request within 90 days.

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

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