[ppl]

Thanks aos, now i gess we can keep this thred on topic, However Tomo may have,as he most often dose! have some insights into Fast regulators.

 

[ppl]

Some Members of this fourm have expressed concern of the amount of Current supplyed by the cascode Current source changing slightly after applying Power to the Current source.

This is normal since all JFETS will have greator leakage current as thay warm up. this is also true of Opamp's that use JFET inputs. The reason that the JFET make sutch a nice and easy to implement Current source is by virtue of one of the drawbacks of JFET's Known as Leakage Current. This is sometimes undesireable, sutch as on the Input of an Opamp. However when using the FET as a method to supply an almost Constant current to a Load this leakage now becomes an attrabute. since the leakage current will change with Tempature and the fact that the Current being supplied will cause a small increce in the Die Tempature of the FET the actual amount of Current supplied to the Load will also go up slightly. with the larger TO-92 and TO-18 Packages of most JFET Transistors this rise in die Tempature is small and as sutch the rise in Current is also small, it is like less than 5% of the Nominal Current.

All Active Devices within any circuit require some time to stabilize and the amount of time is dependent upon anoung other things as the thermal envioment around the Circuit, however 2-5 min. is generaly enough time to allow the circuit to stabilize. by this time the Current source has also stabilized and will remain constant unless the Device is futher heated or Cooled. Tempature changes resulting in parramectric changes to semiconductors is widly Known and Evean the Bipolar transistor will have gain and other paramitors change with temp like the base to emitter voltage (Vbe) and this has also been exploited in Electronic Tempature sensors.