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.

There's no need for a heatsink since the regulator does not dissipate much power.

 

 

 

 

 

 

 

 

 

Here’s a link to the schematic, in pdf format, showing some details of the voltages and operating ranges.

USB_LED_Current_Source_16FEB2012_REV-0.sch

 

This shows the simple package for the LED current source, ready for use in testing the spectra or providing a constant light source on our optical bench.

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