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I have a circuit where I want to have a constant current of 2mA through a variable resistor. I've been told that I could probably use a LM317 as a current regulator, with one resistor on the ouput. But I've read some places that the LM317 takes minimum 5-10mA load to function correctly. How can I achieve a constant current output of 2mA when I don't know the resistance of the variable resistor? The input voltage is about 2.755V. Output voltage doesn't matter, just the current. Here's an image to my feeble attempt at a schematic: The LM317 with the single series resistor between output and adjust input is actually a fixed current source, not a current limiter. You don't need the LM317 to create a current limiter, a few discrete components will do: For a limiting at 2mA you select a 330 Ω resistor for R S E N S E . If there flows 2mA through it Q2 will start to conduct and reduce the base voltage of Q1, so that its current is cut off. edit (re changed question) ...

Simple Ni-Cd and Ni-MH Adjustable Constant Current Project.This is a battery charger circuit with adjustable current for Ni- MH or Ni -Cd. It can be used for a constant current power , which can be set to any value from a few milliamps to about 500 mA . The maximum current is 500 mA , because that is the limit of transistor BC140 . The input voltage must be above 5.25V output voltage , this is due to losses as 1.25V current limit and approximately 4V regulator .  Battery Charger Ni-Cd and Ni-MH Adjustable constant current Circuit Diagram The LM317 regulator is used , it should have a sink . C omponents R1 100Ω resistor VR1 trimpot or potentiometer 500Ω Capacitor C1 0.1μF C2 Capacitor 0.01μF Diode D1 1N4001 Q1 Transistor BC140 IC1 Voltage Regulator LM317

CONSTANT BRIGNESS LED AND MUTE CONTROL ELECTRONIC DIAGRAM The output power of the modules are approximately 220W to 250W into 8? and 350W to 400W into 4?. Complete documentation for the amplifier modules can be found in the documents listed below. AN-1850 LME49830TB Ultra-High Fidelity, High-Power Amplifier Reference Design Although the power supply design is specific to the amplifier modules the concepts and circuit design may be used for any power supply purpose. The power supply is an unregulated design with an option to allow connection to either 120V or 240V mains. The design uses toroidal transformers, a fully integrated bridge, and various rail capacitors for ripple voltage reduction, noise suppression, and to act as high current reservoirs. Additional circuitry to control inrush current on power up and power up/ down Mute control are also included. The topics discussed inside the application note including the introduction, overview, schematic and design, power supply, addition...

An LED is usually a series resistor needed to ensure that the LED does not get too much power. The disadvantage of such a resistor is that the current thus also changes by the LED and the brightness as the voltage changes.  This circuit prevents that, by independent of the voltage, a constant current through the LED.The circuit uses two transistors and two resistors. The circuit can be connected to voltages of from 5 to 24 V.   Constant LED Power Supply Circuit Diagram