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Old 29th October 2009, 06:21 PM   #1
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Default Source for 1.5mA Constant Current Diode in UK / EU?

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
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Old 29th October 2009, 07:56 PM   #2
SY is offline SY  United States
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Why not build your own out of a FET and a resistor? Cheaper, only two parts, and higher performance.
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Old 29th October 2009, 08:28 PM   #3
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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
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Old 29th October 2009, 09:21 PM   #4
SY is offline SY  United States
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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?
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Old 29th October 2009, 09:34 PM   #5
mach1 is offline mach1  Australia
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thermionic, 2SK373 work well in this application. You can set them up for any current up to 5mA.
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