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LED current source based on LT3080, the modern LM317 replacement part, runs off USB or 9V or any voltage in between
This 20mA current source will operate from a USB 5V power supply. Using the LT3080 linear regulator makes it easy to get good voltage headroom. Only 200mV is needed in this version to sense the LED current – the old venerable LM317 required 1.25V just to get started – and that’s not including any drop-out voltage of the pass transistor.
Here’s a link to the schematic, in pdf format, showing some details of the voltages and operating ranges.