Hi,

In the transistor ccs circuits what does K equate to:

http://en.wikipedia.org/wiki/Current_source

K = hFE?

 

From the article:

where K = 1.2 to 2 (so that R1 is low enough to ensure adequate IB),

K needs to change to ensure transistor is in the working area of the transistor, which can be found on the datasheet for your current (Ic). Typically I_B=0.1 x Ic

 

In the middle of the page is this statement:
"where K = 1.2 to 2 (so that R1 is low enough to ensure adequate IB)"
It appears that K is simply a fudge factor that accommodates a wide range of Hfe's.
Minimum base current = Ib and Maximum base current = K*Ib

Another take could be designing for a 'starved' base drive circuit--this might be OK for battery operated devices, but generally a poor design practice.

K and Hfe may be ignored under this condition: Iz = 10* Ib