Biasing PNP BJT

1
Biasing PNP BJT
?
2
PNP BJT Current Source
3
PNP BJT Current Source
?
4
Analyzing PNP BJT Current Source
Applying KVL to the base-emitter circuit of the
Thevenized Equivalent form V1 - IB RB -VEB - IE
RE-VB 0
By replacing IB IE/(1?)
?
?
Thus IC is independent of RC
5
Analyzing PNP BJT Current Source (2)
The circuit works only in the active region Thus
the current source works until IERE ICRC ? V1
VEC (sat)
or
If RC is above this value the transistor will be
driven into saturation
6
Example of PNP BJT Current Source (2)
If V1 15V, R1 9.1 k?, R2 3.9 k?, RE 100
?, ? 75 calculate IB and the upper limit of RC
for the above current source to work properly as
a current source.
k?
?
?
7
Example of PNP BJT Current Source (3)
IC ?IB 71.25 mA
?