# Voltage Divider CE amplifier

#### firebackk

Joined Nov 18, 2020
2
Hello i have this question and was wondering if someone could help me,
Lets say we are given a simple CE amplifier(with voltage divider on base and Rc, Re resistances)
If we are given Ic=3mA , Vcc=20V , β=100, Rth=10kΩ, Vce=10V, how can we calculate the values for R1 and R2?
Also, how can we calculate them if we are not givven the equivalent Rth value?

#### Papabravo

Joined Feb 24, 2006
20,378
Hello i have this question and was wondering if someone could help me,
Lets say we are given a simple CE amplifier(with voltage divider on base and Rc, Re resistances)
If we are given Ic=3mA , Vcc=20V , β=100, Rth=10kΩ, Vce=10V, how can we calculate the values for R1 and R2?
Also, how can we calculate them if we are not givven the equivalent Rth value?
Without a schematic how are we supposed to know WTH you are talking about?
What makes you think the answers are unique?

#### firebackk

Joined Nov 18, 2020
2
this is it

#### djsfantasi

Joined Apr 11, 2010
9,077
This is probably Homework, since you also posted it in homework help. The rules for homework are a little different on this forum. Members cannot answer directly and cannot answer at all unless you post your work.

#### Audioguru again

Joined Oct 21, 2019
6,151
It is simple to calculate the value of Rc.

#### Papabravo

Joined Feb 24, 2006
20,378
If the only thing you are given is Vce and Ic then there are a large number of choices you can make and every one of them will satisfy those requirements. If the transistor is dropping 10 volts (Vce = 10V) then, with a 20V supply, the two resistors will also drop a total of 10 volts and that 10 volt drop can be divided between Rc and Re in a countable infinity of ways.

#### LvW

Joined Jun 13, 2013
1,667
......how can we calculate the values for R1 and R2?
Make the voltage divider as less resistive as possible - with respect to power consumption and input resustance.
The base voltage produced by this divider should be as "stiff" as possible (in particular, less sensitive to the unknown base current).
As a rule of thumb, select a DC current through the divider at least 10 times the necessary base current.