LM337K Adjustable Negative Voltage Regulator

Overview

The LM337K is a member of the LM137 series of adjustable 3-terminal negative voltage regulators. Designed to supply a load current of 1.5A with an output voltage range of -1.2V to -37V, this regulator offers excellent line and load regulation. The device is easy to use and requires only two external resistors to set the output voltage. The LM337K is thermally protected and features current limiting, making it robust against overload conditions. It is ideal for a wide range of applications, including industrial, automotive, and consumer electronics.

Features

• Adjustable Output Voltage: The output voltage can be set from -1.2V to -37V using external resistors.
• High Current Capability: Delivers up to 1.5A of continuous output current.
• Excellent Line and Load Regulation: Ensures stable output voltage despite variations in input voltage or load conditions.
• Thermal Overload Protection: Built-in safeguards prevent damage due to excessive temperature.
• Current Limiting: Protects the regulator and the load from excessive current.
• Wide Operating Temperature Range: Suitable for use in harsh environments.
• TO-3 Package: Robust metal can package for efficient heat dissipation.

Applications

The LM337K is versatile and can be used in a variety of applications, including:

• Power Supplies: Used in adjustable negative voltage power supplies for industrial and laboratory equipment.
• Automotive Electronics: Provides regulated negative voltage for automotive infotainment systems and sensors.
• Consumer Electronics: Suitable for audio amplifiers, televisions, and other home appliances requiring stable negative voltage.
• Industrial Control Systems: Ensures reliable voltage regulation in control circuits and instrumentation.
• Telecommunications: Used in communication devices and networking equipment.

Electrical Characteristics

The following table summarizes the key electrical characteristics of the LM337K under typical operating conditions (unless otherwise specified):

Absolute Maximum Ratings

• Input-Output Voltage Differential (V_IN - V_OUT): 40V
• Power Dissipation (P_D): Internally Limited
• Operating Junction Temperature Range (T_J): -40°C to +125°C
• Storage Temperature Range (T_STG): -65°C to +150°C

Electrical Specifications

• Output Voltage Range: -1.2V to -37V
• Line Regulation (ΔV_OUT/ΔV_IN): 0.01%/V (Typical)
• Load Regulation (ΔV_OUT/ΔI_OUT): 0.1%/A (Typical)
• Minimum Load Current (I_MIN): 3.5mA (Typical)
• Current Limit (I_LIM): 2.2A (Typical)
• Ripple Rejection (RR): 77dB (Typical)

Package Information

The LM337K is available in a TO-3 metal can package, which provides excellent thermal performance and mechanical durability. The package dimensions and pin configuration are as follows:

TO-3 Package Dimensions

• Package Type: TO-3 (Metal Can)
• Mounting Style: Through-Hole
• Weight: Approximately 10g
• Terminal Count: 3 (Input, Output, Adjust)
• Thermal Resistance (Junction-to-Case, R_θJC): 4°C/W

Pin Configuration

• Pin 1 (Adjust): This pin is used to set the output voltage via an external resistor divider network.
• Pin 2 (Input): The input voltage is applied to this pin. A bypass capacitor is recommended for stability.
• Pin 3 (Output): The regulated negative output voltage is provided at this pin.

Typical Application Circuit

A basic adjustable negative voltage regulator circuit using the LM337K is shown below. The output voltage is set by resistors R1 and R2 according to the formula:

V_OUT = -1.25V × (1 + R2/R1) + I_ADJ × R2

Where I_ADJ is the adjust pin current (typically 50µA).

For stable operation, it is recommended to use a 10µF tantalum or aluminum electrolytic capacitor at the output and a 0.1µF ceramic capacitor at the input.

Thermal Considerations

To ensure reliable operation, proper heat sinking is essential, especially when operating at high input-output differentials or high load currents. The TO-3 package is designed to be mounted on a heatsink, and the thermal resistance from junction to ambient (R_θJA) should be minimized to prevent thermal shutdown.

Conclusion

The LM337K is a highly reliable and versatile negative voltage regulator suitable for a wide range of applications. Its adjustable output, robust protection features, and excellent thermal performance make it an ideal choice for designers seeking a stable and efficient negative voltage solution. Whether used in power supplies, automotive systems, or industrial controls, the LM337K delivers consistent performance under varying conditions.