Boban,
Sorry the reply took so long, but yes I am sure...though it does depend on how you rig the CCS, and what sort of CCS it is and where you take the output. IFF it is a MOSFET cascode CCS with near maximum level of battery bias on the lower MOSFET *AND* you take output from the lower FET's source, output Z can indeed get that low. I suspect you are taking output from the plate, which also takes you out of CCS operation of the tube; it is now CCS regulated current minus current supplied to drive the load. Using the lower source as output now leaves the tube running true constant current, it is now the supply delivering regulated plus load current...
cheers,
Douglas
Sorry the reply took so long, but yes I am sure...though it does depend on how you rig the CCS, and what sort of CCS it is and where you take the output. IFF it is a MOSFET cascode CCS with near maximum level of battery bias on the lower MOSFET *AND* you take output from the lower FET's source, output Z can indeed get that low. I suspect you are taking output from the plate, which also takes you out of CCS operation of the tube; it is now CCS regulated current minus current supplied to drive the load. Using the lower source as output now leaves the tube running true constant current, it is now the supply delivering regulated plus load current...
cheers,
Douglas