Lee Cross wrote:
-------------------------------
When you drive your NPN transistor into saturation, a typical value for Vce will be about 0.2V - not very close to 0V when your reference is 1.25V. And Vce is not gauranteed to stay constant.

Steve M. Taylor wrote:
-------------------------------
Its more like 1.2, not .2 volts, so its worse than you said !

Steve, I don't know what kind of transistors you use :o), but even the humble BC547 has a maximum Vce(sat) of 250mV @ Ic=10mA. And as long as the transistor is driven into proper saturation, the temperature effect on Vce(sat) will be negligible.

I do agree with Lee that a MOSFET would be preferable in this situation, but something like a cheap 2N7000 will do the job just as well. Its 5 Ohm Rds(on) means the output voltage will go to 1.3V, using the resistor values Abishek mentions.


Best regards,
Rob.