Hi,
In the transistor ccs circuits what does K equate to:
http://en.wikipedia.org/wiki/Current_source
K = hFE?
In the transistor ccs circuits what does K equate to:
http://en.wikipedia.org/wiki/Current_source
K = hFE?
Constant current sources
- Thread starter Steve1992
- Start date
thatoneguy
- Joined Feb 19, 2009
- 6,359
From the article:
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
"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
