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?

It's an FET connected as a constant current diode.
(Classic jfet and resistor in the source lead.)
Motorola had these for several values of current many years ago.

>
>
> Cheers,
> Don

--
Thomas C. Sefranek  WA1RHP
ARRL Instructor, Technical Specialist, VE Contact.
http://www.harvardrepeater.org
http://hamradio.cmcorp.com/inventory/Inventory.html