78L05K

Updated: 2026-07-17

Overview

The 78L05K is a linear voltage regulator integrated circuit that provides a fixed +5V DC output. As part of the 78xx series of regulators, it is widely used in power supply circuits for electronic devices. The 'L' designation indicates it is the low-current version, typically handling up to 100mA. The regulator maintains a steady 5V output even with fluctuations in input voltage (within specified limits) and load current. Its compact size and simple implementation make it particularly popular in prototyping and small-scale electronic applications where stable low-voltage power is required.

Structure and Working Principle

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The 78L05K consists of a series pass transistor, voltage reference, error amplifier, and thermal protection circuitry all integrated into a single silicon chip. When input voltage is applied (typically 7-20V), the internal circuitry adjusts the pass transistor to maintain exactly 5V at the output. Thermal shutdown protection activates if the junction temperature exceeds safe limits, preventing damage to the device. The regulator requires minimal external components - typically just input and output capacitors for stability. The TO-92 package version has three pins: input, ground, and output, making circuit implementation straightforward.

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Key Features

The 78L05K offers several important features for power regulation applications. Its fixed 5V output has ±5% tolerance under specified operating conditions. The device has built-in short circuit protection and thermal overload protection, enhancing system reliability. With a typical dropout voltage of 1.7V, it requires at least 6.7V input to maintain regulation. The low quiescent current (typically 5mA) makes it suitable for battery-powered applications. Available in various packages including TO-92, SOT-89, and SO-8, it provides flexibility for different PCB layouts and space constraints.

Application Areas

This voltage regulator finds extensive use in consumer electronics, industrial control systems, and embedded devices. Common applications include power supplies for microcontrollers, sensors, and digital logic circuits where stable 5V power is critical. In industrial settings, the 78L05K is often used in control panels, instrumentation, and automation equipment. Its reliability and simplicity make it a standard choice for educational electronics projects and prototyping. The device is also found in automotive electronics (for non-critical systems) and telecommunications equipment where clean power regulation is needed.

Maintenance and Precautions

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Proper implementation of the 78L05K requires attention to several factors. Always maintain the input voltage within specified limits (absolute maximum 30V) to prevent damage. Adequate heat sinking may be necessary if operating near maximum current or with high input voltages. Input and output capacitors should be placed close to the regulator pins to ensure stability and reduce noise. Avoid reverse polarity connections and ensure the ground connection has low impedance. In environments with significant temperature variations, consider derating the maximum current to maintain reliable operation.

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B2B Procurement Guide

When sourcing 78L05K regulators commercially, verify specifications match your requirements. Key parameters to confirm include maximum current (100mA for 78L05), package type, and operating temperature range. For bulk purchases, consider ordering from authorized distributors to ensure genuine components. Lead times may vary, especially for specific package types. Pricing typically decreases significantly for quantities above 1,000 units. Some suppliers offer tape-and-reel packaging for automated assembly processes. Always request current datasheets as specifications may change between manufacturers.