University of Toronto, Physics, Quantum Optics Labs

Alan Stummer, Research Lab Technologist

Multi-LED Driver  A.K.A "Purple Magic"


NOTICE: This webpage and associated files is provided for reference only.  This is not a kit site!  It is a collection of my work here at the University of Toronto in the Physics department. If you are considering using any schematics, designs, or anything else from here then be warned that you had better know something of what you are about to do.  No design is guaranteed in any way, including workable schematic, board layout, HDL code, embedded software, user software, component selection, documentation, webpages, or anything.

All that said, if it says here it works then for me it worked. To make the project work may have involved undocumented additions, changes, deletions, tweaks, tunings, alterations, modifications, adjustments, waving of a wand while wearing a pointy black hat, appeals to electron deities and just plain doing whatever it takes to make the project work.


Ten of the Epitex L405-66-60-550 (or direct from Epitex's website) UV light illuminators are used to pry sticky atoms off of the glass in the BEC/Degenerate Fermions experiment.  Each assembly is rated at 300mA max at about 18-22V (measured) forward voltage.  Although not meeting their specified optical power, ten units are sufficient.

Each of the ten identical constant current circuits uses an opamp to compare the LED current through a 1 Ohm resistor to a setpoint from a pot.  The pot, common to all ten circuits, is driven by a 1.25V band-gap regulator which in turn is enabled by an opto-coupled TTL input.  The pot is a trimpot and needs a screwdriver to adjust it so that it cannot be accidentally changed.

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