I am considering building my own driver for a ~1.5A LED to power a microscope for my research.
For this application, efficiency isn't critical, but because exposure times to the camera can be short (~1ms), stability/lack of ripple is important. Thus buck/boost or other switching regulators, and PWM, are usually avoided here. (Perhaps suitable output filtering would sort this out, but
<500ns [edit: <500 microsec] turn-on/off time is also highly desirable.)
What's the best current regulator for this set-up? (I'll be using a decent switching DC voltage source wall-wart to provide input power to whichever constant-current source I choose.)
One option would be to use an adjustable voltage regulator like a LM317 (but capable of handling more current, so maybe the LT1764 which also has a useful shutdown pin), set up in the standard constant-current mode where current is determined by a resistor between the Vout and Vadj pins. (The voltage between these pins is maintained at ~1.21V for the LT1764, so for 1A you'd want a 1.2-ohm resistor, and for 1.5A a 0.8-ohm resistor.)
The other option might be using a new "one-resistor" voltage regulator like the LT3083, where the voltage is controlled by the resistance-to-ground from a single pin (through which 50 microamps is pushed by varying the voltage: so e.g. a 20kohm resistor induces a 1V output, and a 1-ohm resistor on that output will therefore cause 1 amp to flow).
Here there are two "suggested" constant-current circuits from the datasheet: A constant-current source:
Or a lower-dropout LED driver
The nice thing about the LT3083 is that a 20-kohm potentiometer can be used to adjust current, unlike the LT1674, where you'd need a 20-ohm pot (rather harder to source) to adjust between ~.1A and 1.5A. But I'm not sure which of the two suggested driver circuits for the LT3083 would be more resistant to ripple from the input voltage source, if either. And I don't know if this is a bad idea for other reasons compared to the more standard regulators. (e.g. if the adj pin is left floating, it looks like the LT3083 will probably drive the voltage way up and fry the LED. So if the pot fails or a connection breaks, this could be bad news.)
So, anyone have suggestions for the best option?