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thermionic 29th October 2009 07:21 PM

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

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.


SY 29th October 2009 08:56 PM

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

thermionic 29th October 2009 09:28 PM

Thanks, SY. I could build a current source like this one: 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:

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


SY 29th October 2009 10:21 PM

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 29th October 2009 10:34 PM

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

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