The 78Lxx series is a family of fixed-output linear voltage regulators designed for low-current applications. Often called “universal” regulators, they are found in almost every type of electronic device, from industrial equipment to household appliances. Their primary job is to take a fluctuating or high input voltage and provide a rock-steady, clean output.
This guide explores the full range of the 78Lxx family, covering everything from the popular 5V version to the high-voltage 24V models.
Key Features of the 78Lxx Family
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Wide Voltage Range: Available in multiple fixed output voltages to suit any circuit.
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High Input Tolerance: Capable of handling input voltages up to 30V–35V, much higher than LDO regulators.
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Ease of Use: Requires only two external capacitors to function perfectly.
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Robust Protection: Includes built-in thermal shutdown and internal current limiting to prevent the chip from burning out during a fault.
The 78Lxx Voltage Lineup
The “xx” in the part number represents the output voltage. While they all look the same physically, their internal tuning is different.
1. Common Low-Voltage Models
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78L05 (5V)/78L06 (6V): The industry standard for digital logic, microcontrollers, and sensors.
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78L08 (8V): Frequently used in audio equipment and older analog signaling.
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78L09 (9V)/78L10 (10V): The perfect choice for replacing 9V batteries in portable gadgets.
2. High-Voltage Models
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78L12 (12V): Used for powering relays, small DC fans, and LED strings.
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78L15 (15V): Common in industrial automation and operational amplifier (Op-Amp) power rails.
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78L24 (24V): Used in specialized high-voltage communication interfaces.
Available Packages
Depending on your PCB design, the 78Lxx is available in several form factors:
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TO-92 (Through-Hole): The most common “transistor-style” package used by hobbyists and for breadboarding.
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SOIC-8 (Surface Mount): A standard 8-pin SMD package used for automated high-volume production.
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SOT-89 (Surface Mount): A flat SMD package with a thermal pad for better heat management in compact designs.
78Lxx TO-92 CAD Model
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78Lxx SOIC-8 CAD Model 78Lxx SOT-89 CAD Model
Technical Specification Overview
| Parameter | Value (Standard) |
| Input Voltage (Max) | 30V (for 5V–9V models) / 35V (for 12V–24V) |
| Output Current | 100mA (Max) |
| Dropout Voltage | ~1.7V to 2.0V |
| Quiescent Current | 3mA – 6mA |
| Operating Temp | 0°C to 125°C |
Pro-Tips for Universal Integration
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The “2-Volt” Rule: Always ensure your input voltage is at least 2V higher than your target output. For a 78L05, you need at least 7V input.
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Polarity Check: Remember that the 78Lxx is for Positive voltages. If you are designing a dual-rail power supply and need a negative version, use the 79Lxx series (e.g., 79L05 for -5V).
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Thermal Management: Even though they are “universal,” they are not for high power. If you try to drop 24V down to 5V at 100mA, the chip will get very hot (P = (Vin – Vout) \ I).
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Capacitor Choice: Use ceramic capacitors (0.33μF on input, 0.1μF on output) to ensure the regulator doesn’t “whistle” (oscillate) at high frequencies.
Alternatives for 78Lxx
LM317L (Adjustable version), AMS1117 (LDO version), LP2950 (Low Quiescent), MCP1700