LM234 3-Terminal Adjustable Current Source

Overview

The LM234, along with its variants LM134 and LM334, is a precision 3-terminal adjustable current source designed for a wide range of applications requiring stable and adjustable current regulation. This component offers an exceptional operating current range of 10,000:1, excellent current regulation, and a broad dynamic voltage range from 1V to 40V. The current is easily set using a single external resistor, making it highly versatile and simple to integrate into various circuits. The LM234 is particularly notable for its floating current source capability, eliminating the need for separate power supply connections.

One of the standout features of the LM234 is its ability to handle reverse voltages of up to 20V while drawing minimal current, making it suitable for AC applications where it can function as both a rectifier and a current source. The device's sense voltage, which determines the operating current, is 64mV at 25°C and scales proportionally with absolute temperature (in Kelvin). This characteristic allows for precise temperature-dependent current generation, with a typical temperature coefficient of +0.33%/°C. Additionally, the LM234 can achieve zero-drift operation with minimal additional circuitry, further enhancing its precision in temperature-sensitive applications.

Features

• Wide Operating Voltage Range: Functions reliably from 1V to 40V, accommodating a variety of power supply conditions.
• Adjustable Current Source: Current is set using a single external resistor, simplifying design and implementation.
• High Current Range: Offers a 10,000:1 operating current range, providing flexibility for diverse applications.
• Excellent Current Regulation: Maintains stable current output even with fluctuations in supply voltage or load conditions.
• Floating Current Source: No separate power supply connections are required, enhancing ease of use in floating applications.
• Reverse Voltage Tolerance: Can withstand reverse voltages up to 20V while drawing only minimal current, enabling use in AC circuits.
• Temperature Proportional Operation: Sense voltage is directly proportional to absolute temperature, allowing for temperature-compensated designs.
• Low Initial Current Error: Initial current accuracy of ±3% ensures precise performance right out of the box.
• Zero-Drift Capability: Can be configured for zero-drift operation with minimal additional components.

Applications

The LM234's versatility and precision make it suitable for a wide array of applications, including but not limited to:

• Current Sources and Sinks: Ideal for creating stable current sources or sinks in analog circuits.
• Temperature Sensors: The temperature-proportional sense voltage allows for accurate temperature sensing and compensation.
• Battery Charging: Can be used in constant-current charging circuits for batteries.
• LED Drivers: Provides stable current drive for LEDs, ensuring consistent brightness.
• AC Signal Processing: Functions as both a rectifier and current source in AC applications due to its reverse voltage tolerance.
• Precision Amplifiers: Useful in biasing and compensation circuits for operational amplifiers and other precision analog components.
• Industrial Control Systems: Suitable for use in control loops and instrumentation requiring stable current references.

Electrical Characteristics

The following table summarizes the key electrical characteristics of the LM234 under typical operating conditions (unless otherwise specified):

• Operating Voltage Range: 1V to 40V
• Operating Current Range: 10,000:1 (e.g., 1µA to 10mA)
• Initial Current Accuracy: ±3%
• Sense Voltage (at 25°C): 64mV
• Temperature Coefficient: +0.33%/°C (proportional to absolute temperature)
• Reverse Voltage Tolerance: Up to 20V (with minimal leakage current)
• Power Dissipation: Dependent on external resistor and operating conditions (refer to datasheet for detailed limits)

Package Information

The LM234 is available in several industry-standard packages, ensuring compatibility with a wide range of PCB designs and assembly processes. The following packages are commonly available:

• TO-92: A through-hole package suitable for prototyping and low-power applications.
• SOT-23: A small surface-mount package ideal for space-constrained designs.
• SOIC-8: A surface-mount package offering a balance of size and ease of handling for automated assembly.

For detailed mechanical drawings, dimensions, and recommended PCB footprints, refer to the manufacturer's datasheet.

Conclusion

The LM234 is a highly versatile and precise adjustable current source, offering exceptional performance across a wide range of operating conditions. Its simplicity, combined with advanced features like temperature-proportional operation and reverse voltage tolerance, makes it an excellent choice for designers working on precision analog circuits, temperature sensing, and power management applications. Whether used in industrial control systems, consumer electronics, or experimental setups, the LM234 delivers reliable and stable current regulation with minimal external components.