LM123 Technical Summary

LM123 Three-Terminal Positive Voltage Regulator

Overview

The LM123 is a high-performance, three-terminal positive voltage regulator designed to deliver a fixed 5V output with exceptional accuracy and load-driving capability. This component utilizes advanced circuit design and manufacturing techniques to provide stable 5V regulation at currents up to 3A, making it suitable for demanding power supply applications. The device features internal current limiting, thermal shutdown, and safe-area compensation for robust operation under various load conditions.

Available in standard transistor packages, the LM123 offers designers a reliable solution for systems requiring precise voltage regulation. The A-version of this regulator guarantees 1% initial output voltage accuracy, ensuring consistent performance in precision applications.

Key Features

Fixed 5V Output: Preset voltage regulation eliminates the need for external voltage-setting components
High Current Capability: 3A continuous output current with proper heat sinking
Exceptional Accuracy: A-version guarantees 1% initial output voltage tolerance
Built-in Protection: Internal current limiting and thermal shutdown protection
Wide Operating Temperature Range: Suitable for industrial applications
Low Dropout Voltage: Maintains regulation with small input-output differential
Stable Operation: Internal compensation ensures stability with minimal external components
Safe-Area Compensation: Protects the regulator under overload conditions

Applications

The LM123 is designed for use in a wide range of electronic systems requiring stable 5V power:

Digital Systems: Power supply regulation for TTL and CMOS logic circuits
Microprocessor Power: Voltage regulation for CPU and peripheral components
Industrial Controls: Reliable power for control systems and instrumentation
Automotive Electronics: Voltage stabilization for vehicle electronic systems
Test Equipment: Precision voltage reference for measurement devices
Embedded Systems: Power management for microcontroller-based designs
Peripheral Devices: Regulation for disk drives, printers, and other computer peripherals

Electrical Characteristics

Absolute Maximum Ratings

Input Voltage: 35V (maximum)
Power Dissipation: Internally limited (see thermal characteristics)
Operating Junction Temperature Range: -40°C to +125°C
Storage Temperature Range: -65°C to +150°C

Electrical Specifications

(TA = 25°C, IO = 500mA, VI = 10V unless otherwise specified)

Output Voltage: 4.95V to 5.05V (A version, 1% tolerance)
Line Regulation: 10mV (VI = 7V to 25V)
Load Regulation: 15mV (IO = 5mA to 3A)
Quiescent Current: 10mA (typical)
Quiescent Current Change: 1.2mA (VI = 7V to 25V)
Dropout Voltage: 2V (maximum at IO = 3A)
Output Noise Voltage: 40μV (10Hz to 100kHz)
Ripple Rejection: 68dB (120Hz)
Output Impedance: 15mΩ (1kHz)

Package Information

The LM123 is available in several industry-standard packages to accommodate different application requirements:

TO-220 Package

Package Type: TO-220-3 (KTE)
Dimensions: 10.0mm x 15.0mm x 4.5mm (body)
Lead Spacing: 2.54mm (between pins)
Mounting: Through-hole with thermal tab
Thermal Resistance: Junction-to-Case: 3°C/W

TO-263 Package (D2PAK)

Package Type: TO-263-3 (D2PAK)
Dimensions: 10.28mm x 9.65mm x 4.57mm (body)
Mounting: Surface mount with exposed thermal pad
Thermal Resistance: Junction-to-Case: 3°C/W

Thermal Considerations

Proper thermal management is critical when operating the LM123 at high current levels. The following guidelines should be observed:

Always use appropriate heat sinking for currents above 1A
Maintain junction temperature below 125°C for reliable operation
For surface mount applications, ensure adequate PCB copper area for heat dissipation
Thermal vias should be used when implementing surface mount designs

Design Considerations

Input Capacitor

An input capacitor is recommended when the regulator is located more than 3 inches from the power supply filter. A 0.33μF ceramic or 1μF tantalum capacitor is typically sufficient.

Output Capacitor

While not required for stability, an output capacitor improves transient response. A 1μF tantalum or 25μF aluminum electrolytic capacitor is recommended.