Source for 1.5mA Constant Current Diode in UK / EU?

[thermionic]

Hi,

I need to find some constant current diodes for the LTP collectors on the front end of a pwr amp. They're quoted at 1.5mA and need to be able to handle up to 100v. I can't find any 1.5mA items @ Farnell / RS / Cricklewood. Is there anyone else?

Thanks in advance.

Justin

[SY]

Why not build your own out of a FET and a resistor? Cheaper, only two parts, and higher performance.

[thermionic]

Thanks, SY. I could build a current source like this one: http://sound.westhost.com/ab-f5-2.gif However, PCB space is limited, so it'd have to be kludged in there. I've found that the 1N5302 should do the job and can find them in the UK: http://www.centralsemi.com/PDFs/prod...N5283-5314.pdf

What's the advantage of making one from a Jfet + R?

J

[SY]

Well, one advantage is that you can buy them easily and they're cheaper.

All a CCS diode is is a FET with the gate and source shorted together and running at the FET's Idss. If you use a resistor to bias the FET to a lower current, the drain impedance rises (what you want for a CCS). So, lower cost, only two parts (a FET and a resistor), higher performance... why bother with a CC diode?

[mach1]

thermionic, 2SK373 work well in this application. You can set them up for any current up to 5mA.