LM79LXX Series Negative Voltage Regulator

Overview

The LM79LXX series is a family of 3-terminal negative voltage regulators designed to provide fixed output voltages of -5V, -12V, and -15V with an output current capability exceeding 100 mA. These regulators are engineered using advanced computer-aided design techniques to optimize both thermal and electrical performance. The series is particularly noted for its excellent transient response and high regulation accuracy, making it suitable for a wide range of applications requiring stable negative voltage supplies.

Key advantages of the LM79LXX series include robust performance with minimal external components, requiring only a 0.1 µF output compensation capacitor for stable operation. The devices are designed to deliver reliable performance in various environmental conditions, ensuring consistent voltage regulation.

Features

• Fixed Output Voltages: Available in -5V, -12V, and -15V configurations.
• High Output Current: Capable of delivering over 100 mA of continuous output current.
• Excellent Line Regulation: Maximum line regulation of 0.07% (ΔV_O/V).
• Low Dropout Voltage: Optimized for efficient operation with minimal power loss.
• Thermal and Electrical Optimization: Designed using advanced computer techniques for superior performance.
• Transient Response: Exhibits excellent transient response with minimal output capacitance (0.1 µF).
• Internal Thermal Overload Protection: Safeguards the device against excessive temperature.
• Short-Circuit Protection: Built-in protection against output short circuits.

Applications

The LM79LXX series is widely used in applications requiring stable negative voltage supplies. Some common applications include:

• Power Supplies: Used in linear power supplies for analog and digital circuits.
• Consumer Electronics: Suitable for audio amplifiers, televisions, and other home appliances.
• Industrial Equipment: Provides regulated voltage for control systems and instrumentation.
• Telecommunications: Used in communication devices and networking equipment.
• Automotive Electronics: Supports voltage regulation in automotive control modules.
• Test and Measurement: Ideal for precision measurement equipment requiring stable voltage references.

Electrical Characteristics

The following table summarizes the key electrical specifications for the LM79LXX series under typical operating conditions (T_A = 25°C, unless otherwise specified).

Absolute Maximum Ratings

• Input Voltage (V_IN): -35V
• Operating Junction Temperature (T_J): 0°C to +125°C
• Storage Temperature Range (T_STG): -65°C to +150°C
• Maximum Power Dissipation (P_D): Internally limited by thermal protection

Electrical Specifications

• Output Voltage Tolerance: ±4% (for -5V, -12V, and -15V variants)
• Line Regulation: 0.07% (typical), 0.1% (maximum)
• Load Regulation: 0.1% (typical), 0.3% (maximum)
• Dropout Voltage: 1.7V (typical at 100 mA load)
• Quiescent Current: 5 mA (typical)
• Ripple Rejection: 60 dB (typical at 120 Hz)
• Output Noise Voltage: 40 µV (typical, 10 Hz to 100 kHz)

Package Information

The LM79LXX series is available in multiple package options to accommodate different application requirements. The following packages are commonly used:

TO-92 Package

• Package Type: Plastic, through-hole
• Pin Configuration:
  • Pin 1: Input (V_IN)
  • Pin 2: Ground (GND)
  • Pin 3: Output (V_OUT)
• Thermal Resistance (θ_JA): 160°C/W
• Dimensions: 4.95 mm x 4.95 mm x 4.95 mm

SOT-89 Package

• Package Type: Surface-mount
• Pin Configuration:
  • Pin 1: Ground (GND)
  • Pin 2: Output (V_OUT)
  • Pin 3: Input (V_IN)
• Thermal Resistance (θ_JA): 90°C/W
• Dimensions: 4.5 mm x 2.5 mm x 1.5 mm

Typical Application Circuit

The LM79LXX requires minimal external components for operation. A basic application circuit includes:

• Input Capacitor (C_IN): 0.33 µF (recommended for stability)
• Output Capacitor (C_OUT): 0.1 µF (required for transient response)

The input capacitor helps filter high-frequency noise, while the output capacitor ensures stability and improves transient response. For optimal performance, place these capacitors as close as possible to the regulator pins.

Conclusion

The LM79LXX series of negative voltage regulators offers a reliable and efficient solution for applications requiring stable negative voltage supplies. With its robust design, excellent regulation, and protection features, it is well-suited for a wide range of electronic systems. Whether used in consumer electronics, industrial equipment, or telecommunications, the LM79LXX provides consistent performance with minimal external components.