Transistor CCS resistor value calculation.

[Alistair D]

Instead of a zener use one or more red LEDs in series. The +ve temperature co-efficient of an LED closely matches the -ve co-efficient of the transistor's B-E junction. 

I have built a couple of CCSs using this method and they worked fine. I never tested the temperature stability to see if LEDs were better than zeners, the word of the gurus was good enough for me.

Al