Hello all,

I'm just curious how the appropriate values of R1 and R2 are calculated for this specific problem.

My work is attached.

Any ideas?

 

Voltage divider must deliver 0.8V to the base.
And the current which will flow through voltage divider must be larger then
Ib_max = Ic/Hfe_min = 0.5mA/200 = 2.5uA
So we can assume I = 20 * Ib_max = 50uA
R1 = ( 9V - 0.8V) / ( 50uA + 2.5uA) = 156K = 160K
R2 = 0.8V/50uA = 16K


EDIT
And it seems to me that Rout should be less than 5K

 

Voltage divider must deliver 0.8V to the base.
And the current which will flow through voltage divider must be larger then
Ib_max = Ic/Hfe_min = 0.5mA/200 = 2.5uA
So we can assume I = 20 * Ib_max = 50uA
R1 = ( 9V - 0.8V) / ( 50uA + 2.5uA) = 156K = 160K
R2 = 0.8V/50uA = 16K


EDIT
And it seems to me that Rout should be less than 5K

Whoops, I edited that typo on the hard copy and not my digital one.

It is simply a typo.