LM350K Adjustable 3-Terminal Positive Voltage Regulator

Overview

The LM350K is a member of the LM150 series of adjustable 3-terminal positive voltage regulators, designed to deliver a robust output current exceeding 3A across a wide voltage range of 1.2V to 33V. This regulator is engineered for simplicity and reliability, requiring only two external resistors to configure the output voltage. Its performance in line and load regulation rivals that of discrete designs, making it an excellent choice for both prototyping and production applications. The LM350K is packaged in standard transistor packages, ensuring ease of mounting and integration into various circuit designs.

Key Features

• High Output Current: Capable of supplying more than 3A of continuous output current.
• Wide Adjustable Output Range: Output voltage can be set from 1.2V to 33V using external resistors.
• Excellent Line and Load Regulation: Comparable to discrete regulator designs, ensuring stable performance under varying conditions.
• Thermal Overload Protection: Built-in safeguards prevent damage due to excessive heat.
• Short-Circuit Protection: Protects the regulator and connected components in case of a short circuit.
• Standard Transistor Package: Easy to mount and suitable for a variety of applications.
• Low Dropout Voltage: Efficient operation with minimal voltage loss.

Applications

The LM350K is versatile and can be used in a wide range of applications, including but not limited to:

• Power Supplies: Adjustable voltage supplies for laboratory equipment, industrial controls, and consumer electronics.
• Battery Chargers: Efficient charging circuits for lead-acid, NiMH, and Li-ion batteries.
• Motor Control: Voltage regulation in DC motor speed controllers.
• Audio Amplifiers: Stable voltage rails for high-fidelity audio systems.
• LED Drivers: Constant voltage sources for LED lighting applications.
• Embedded Systems: Reliable power management for microcontrollers and sensors.

Electrical Characteristics

The following table summarizes the key electrical specifications of the LM350K under typical operating conditions (unless otherwise noted):

• Output Voltage Range: 1.2V to 33V
• Output Current: 3A (minimum guaranteed)
• Line Regulation: 0.01% / V (typical)
• Load Regulation: 0.1% / A (typical)
• Dropout Voltage: 2.5V (typical at 3A)
• Operating Junction Temperature: -40°C to +125°C
• Thermal Resistance (Junction-to-Case): 3°C/W (typical)

Absolute Maximum Ratings

• Input-Output Voltage Differential: 35V
• Power Dissipation: Internally limited by thermal protection
• Storage Temperature Range: -65°C to +150°C
• Lead Temperature (Soldering, 10 sec): 300°C

Package Information

The LM350K is available in a standard TO-3 transistor package, which is robust and suitable for high-power applications. The package dimensions and pin configuration are as follows:

• Package Type: TO-3 (Metal Can)
• Dimensions: 10.67mm (diameter) x 9.65mm (height)
• Weight: Approximately 6.5 grams
• Pin Configuration:
  • Pin 1: Adjust (Connects to external resistor divider)
  • Pin 2: Output (Regulated voltage output)
  • Pin 3: Input (Unregulated input voltage)

Thermal Considerations

Due to its high current capability, the LM350K may generate significant heat during operation. Proper heat sinking is essential to maintain performance and reliability. The thermal resistance of the TO-3 package is low, but additional heat sinking may be required for high-current applications or elevated ambient temperatures.

Typical Application Circuit

A basic adjustable voltage regulator circuit using the LM350K is shown below. The output voltage is set by the ratio of two resistors, R1 and R2, connected between the output and adjust pins.

• R1: 240Ω (typical value for stability)
• R2: Calculated based on desired output voltage (Vout = 1.25V × (1 + R2/R1))
• Input Capacitor (C1): 0.1µF to 1µF (recommended for noise reduction)
• Output Capacitor (C2): 1µF to 10µF (improves transient response)

Conclusion

The LM350K is a highly reliable and versatile voltage regulator, offering exceptional performance for a wide range of applications. Its ability to deliver high current with minimal external components makes it a preferred choice for designers seeking efficiency and simplicity. Whether used in power supplies, battery chargers, or motor control systems, the LM350K provides stable and adjustable voltage regulation with robust protection features.