LM109K

Overview

The LM109K is a fixed 5-volt linear voltage regulator manufactured by Texas Instruments. It provides an output current exceeding 1 ampere and features internal thermal overload protection to prevent overheating during fault conditions. The device requires no external components for basic operation, simplifying circuit design. It is designed for local regulation on digital logic cards to eliminate distribution problems associated with single-point regulation. The regulator includes current limiting to protect against short circuits and offers good rejection of load or line transients typical in TTL logic applications.

Feature Summary

• Internal thermal overload protection prevents damage from excessive heat dissipation
• Current limiting protects the device during short-circuit or overload events
• No external components required for standard fixed-voltage regulation operation
• Designed for local regulation on digital logic cards to improve stability

Applications

• Local regulation on digital logic cards
• TTL and DTL compatible power supply circuits
• Precision regulators using the circuit as a control element
• Applications requiring blowout-proof voltage regulation

Procurement Notes

Verify the specific package type and suffix when ordering, as the LM109 series is available in multiple physical packages such as TO-39 and solid-kovar headers. Confirm that the 'K' suffix corresponds to the intended mechanical form factor for your assembly process. Ensure adequate heat sinking is provided if operating near maximum current limits to maintain thermal safety margins.

Selection Notes

Select the LM109K when a robust, high-current 5-volt regulator is needed for digital logic systems. Its internal protections make it suitable for environments where short circuits or thermal stress are potential risks. Consider the physical package constraints and thermal requirements of the application to ensure the device can dissipate heat effectively without external bypassing, although output bypassing may improve transient response.

Part Context

The LM109 series consists of complete 5-volt regulators fabricated on a single silicon chip. They are engineered to provide reliable voltage regulation for digital logic families like TTL and DTL. The series emphasizes ease of use by minimizing external component requirements while offering significant current handling capabilities and built-in safety features against thermal and electrical faults.

Replacement Considerations

Public confirmed substitute part numbers: LM109H/NOPB, LM109QML.