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