Cascoded MOSFET with 2015 Jung Universal Regulator

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I'm sure google has the answer to this quetion, but I cannot find the question.

I would like to use a MOSFET cascode, as shown here (last page Fig 1):

http://waltjung.org/PDFs/AX_WJ_Interview.pdf

I'd like to use that cascode in this regulator:

http://www.waltjung.org/PDFs/UnivReg_122714.pdf

In the second article Mr. Jung points out that with a single MOSFET the input voltage must be at least 8V or higher than the output voltage (for DN2540).

Assuming DN2540 cascode, 0.15A per regulator, and 15V output, what should the input voltage be?
 
In the cascode the lower fet is the CCS and the upper one gives a voltage shift plus more ore less constant voltage for the lower one.
Total voltage needed is Vgs(lower)+Vgs(upper)+Vds(upper), don't think you need more then with one fet, probably even less.
Mona
 

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