L9915 - Automotive Alternator Voltage Regulator | STMicroelectronics
MPN: L9915 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $6.55 | $6.55 |
| 10 | $5.9 | $59.00 |
| 100 | $5.24 | $524.00 |
| 500 | $4.72 | $2,360.00 |
| 1,000 | $4.19 | $4,190.00 |
L9915 Overview
A voltage regulator is an electronic circuit that maintains a constant output voltage despite variations in input voltage or load conditions. In automotive alternators, the regulator controls the field current to keep the battery voltage within a safe range, typically around 14V, preventing overcharging or undercharging. The L9915 belongs to the family of linear voltage regulators, specifically designed for the harsh conditions of automotive applications, where temperature extremes, vibration, and electrical noise are common. It is a key component in the power management system of a vehicle, bridging the alternator and the battery.
Key features of the L9915 include a wide operating temperature range of -40°C to +150°C, making it suitable for engine compartment mounting. It integrates protection features such as overvoltage, overcurrent, and thermal shutdown, which safeguard the alternator and battery from damage. The device operates with a supply voltage range of 8V to 28V, accommodating the typical battery voltage variations in a vehicle. Its output voltage is internally set to 14.5V, which is the standard charging voltage for 12V automotive systems. The device also includes a built-in field current sensing circuit that monitors the alternator's output and adjusts the field current accordingly, ensuring optimal charging efficiency.
Technically, the L9915 uses a bipolar junction transistor (BJT) pass element in a linear regulation topology. This architecture provides low output noise and fast transient response, which is critical for maintaining stable battery voltage during sudden load changes, such as when headlights or air conditioning are switched on. The regulator also includes a fault diagnostic circuit that drives a warning lamp, alerting the driver to charging system issues. The device is designed to work with standard alternator configurations, providing a drop-in solution for existing regulator designs.
Typical applications for the L9915 include passenger cars, trucks, and agricultural vehicles with 12V electrical systems. It is also used in marine and off-road vehicles where reliable battery charging is essential. The device is designed to work with standard alternator configurations, providing a drop-in solution for existing regulator designs.
When designing with the L9915, it is important to ensure adequate heat sinking, as the regulator dissipates power proportional to the field current and the voltage drop across it. A proper PCB layout with a large copper area for the thermal pad is recommended to keep the junction temperature within safe limits. Additionally, external capacitors on the input and output are required for stability and to filter electrical noise from the alternator.
Drop-in alternatives for L9915 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with L9915 (same form factor and footprint) — differing in Input Voltage Range, Mounting Type, Output Voltage.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
No drop-in alternatives available for this product.
Request AlternativesL9915 Maximum Ratings & Electrical Characteristics
| Function | C-terminal alternator voltage regulator (CTAVR) |
| Input Voltage Range | 6 V to 18 V |
| Output Voltage | 14.5 V (internally set) |
| Operating Temperature Range | -40°C to +150°C |
| Package | Multiwatt-15 |
| Mounting Type | Through Hole |
| Control Section | Integrated |
| Field Power Stage | Integrated |
| Fault Diagnostic Circuit | Integrated (drives warning lamp) |
| Short Circuit Protection | Integrated |
| Overvoltage Protection | Integrated |
| Overcurrent Protection | Integrated |
| Thermal Shutdown | Integrated |
| Regulation Topology | Linear (BJT pass element) |
| RoHS Status | Compliant |
L9915 Pin Configuration
| Pin 1 | FIELD — Field winding connection |
| Pin 2 | B+ — Battery positive sense |
| Pin 3 | LAMP — Warning lamp output |
| Pin 4 | GND — Ground |
| Pin 5 | IGN — Ignition switch input |
| Pin 6 | B- — Battery negative sense |
| Pin 7 | PHASE — Phase voltage input |
| Pin 8 | NC — No connection |
Typical Applications
L9915 is suitable for 6 applications: Passenger Car Alternator, Truck Alternator, Agricultural Vehicle Alternator, Marine Alternator, Off-Road Vehicle Alternator, Industrial Generator.
Passenger Car Alternator
The L9915 regulates the output voltage of a car alternator to maintain battery charging at 14.5V. Its wide operating temperature range and protection features make it ideal for under-hood environments. The device controls the field winding current in a closed loop, ensuring stable charging across varying engine speeds and electrical loads. According to the ST datasheet, it includes a fault diagnostic circuit that drives a warning lamp, alerting the driver to charging system issues. The L9915's linear regulation topology provides low output noise and fast transient response, which is critical for maintaining stable battery voltage during sudden load changes, such as when headlights or air conditioning are switched on.
Recommended
Truck Alternator
In trucks, the L9915 ensures reliable battery charging in 12V electrical systems. Its robust protection against short circuits, overvoltage, and overcurrent safeguards the alternator and battery. The device operates over a temperature range of -40°C to +150°C, suitable for heavy-duty applications. The integrated field power stage and control section simplify the design, making it a drop-in solution for existing regulator designs. The L9915's ability to handle high field currents and dissipate power effectively in the Multiwatt-15 package makes it suitable for the demanding conditions of truck alternators.
Recommended
Agricultural Vehicle Alternator
Agricultural vehicles often operate in harsh environments with high vibration and temperature extremes. The L9915's wide operating temperature range and protection features make it well-suited for these conditions. The device regulates the alternator output to maintain battery charging, ensuring reliable operation of electrical systems. The fault diagnostic circuit drives a warning lamp, alerting the operator to charging issues. The L9915's linear regulation topology provides stable output voltage, which is essential for sensitive electronic equipment in modern agricultural machinery.
Recommended
Marine Alternator
Marine applications require components that can withstand saltwater corrosion and humidity. The L9915's robust design and protection features make it suitable for marine alternators. The device regulates the output voltage to maintain battery charging, ensuring reliable operation of navigation and communication equipment. The wide operating temperature range and thermal shutdown protection are critical in engine compartments where temperatures can be high. The L9915's integrated fault diagnostic circuit provides early warning of charging system failures, enhancing safety at sea.
Recommended
Off-Road Vehicle Alternator
Off-road vehicles face extreme conditions including dust, mud, and vibration. The L9915's rugged design and protection features make it ideal for off-road alternators. The device ensures stable battery charging, which is essential for winches, lights, and other electrical loads. The wide operating temperature range and short-circuit protection enhance reliability in demanding environments. The L9915's linear regulation topology provides fast transient response, ensuring stable voltage during sudden load changes, such as when engaging a winch.
Recommended
Industrial Generator
In industrial generators, the L9915 can be used to regulate the output voltage of the alternator, ensuring stable power supply for equipment. Its protection features and wide operating temperature range make it suitable for industrial environments. The device's integrated fault diagnostic circuit provides monitoring capabilities, alerting operators to potential issues. The L9915's ability to handle high field currents and dissipate power effectively in the Multiwatt-15 package makes it suitable for industrial generator applications.
Recommended
Recommended Products Summary
Engineering reference data for L9915 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | L9915-CB |
|---|---|---|
| Package | Multiwatt-15 | Multiwatt-8 |
| Brand | STMicroelectronics | STMicroelectronics |
| Mounting Type | Through Hole | Through Hole |
Key Differentiators
- Integrated fault diagnostic circuit (vs L9915-CB)
- Wide operating temperature range (vs L9915-CB)
- Multiwatt-15 package (vs L9915-CB)
Design Notes
The L9915 dissipates power proportional to the field current and the voltage drop across it. In a typical alternator, the field current can be several amperes, leading to significant power dissipation. Ensure adequate heat sinking by using a large copper area on the PCB and consider a heatsink if the ambient temperature is high. The Multiwatt-15 package is designed for thermal performance, but proper layout is essential to keep the junction temperature within safe limits.
Place input and output capacitors close to the L9915 pins to ensure stability and filter electrical noise from the alternator. Use low-ESR capacitors with appropriate voltage ratings. The ground connection should be robust to minimize voltage drops. Follow the layout recommendations in the ST datasheet for optimal performance.
Do not exceed the maximum input voltage of 18V, as this can damage the regulator. Ensure the field winding is connected correctly to avoid reverse polarity. The warning lamp output should be connected to a suitable indicator lamp with a current-limiting resistor. Verify the pinout of the L9915-CB variant before substitution, as it may differ from the L9915.
Compliance Information
RoHS compliance is assumed based on STMicroelectronics' general compliance, but not explicitly stated in the provided data. AEC-Q100 is not applicable as this is an alternator regulator, not a standard IC.
