You can make a current limiter out of an LM317 with a resistor across the "Output" and "Reference" terminals, if they just packaged such a die with the resistor as a 2-terminal package, that sounds about like what you have there. Nice discrete, it makes GOOD sense to use those for LED's, wish I had some here! Great for a number of applications. Car tail light LED units, for one. Related question; Wonder what happens when one parallels these devices? I'd think the "conductances" would add, 2 paralleled 20mA units should let about 40mA flow, but I haven't tested it yet. Should get to that some day Mark Don Holtz wrote: > > Hello: > > I was recently in Japan, and visited Akihabara. While there I picked up a > handful of really bright White LEDs. With each LED the vendor also gave me > an interesting discrete device that looks like a standard small-signal > glass encapsulated diode. > > I don't speak Japanese but I was able to get the vendor to draw a simple > schematic, since I was confused about the device. > > The device appears to be a "current regulating diode" analogous to a > zener.... 15mA! > > In this instance the LED and "current regulating diode" are placed in > series, and the combination can be driven with a voltage between 4V and 20V. > > Further testing shows that below the "turn on" current level the device has > a fairly low impedance (approx. 200ohm), above the "turn on" current level > the device has a fairly high impedance of more than 100Kohm. > > The only marking on the device is E153. > > The symbol the vendor used in the schematic was a circle with a bar, kind > of like an arrow head with a bar (for a diode). > > What is this device? Am I missing something simple? > > Cheers, > Don -- I ship small packages for small businesses, world-wide. (And for private individuals at cost, just ask.)