# Thevenin's theorem BJT derivation

#### cikalekli

Joined Dec 10, 2020
103
Here, I want to use Thevenin with those 2 resistors in the base.

How can I combine those two resistors with thevenin or do you have any other better idea to combine them? (circled with red in the picture)

(PS: I don't ask the solution of the question. I'm only asking individually the calculation of those two resistors. Thank you.)

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#### BobTPH

Joined Jun 5, 2013
3,316
Pretend the base is not connected and calculate the voltage at the junction. Then it is equivalent of a source at that voltage with a series resistor that us the parallel combination of the two.

Bob

#### cikalekli

Joined Dec 10, 2020
103
Pretend the base is not connected and calculate the voltage at the junction. Then it is equivalent of a source at that voltage with a series resistor that us the parallel combination of the two.

Bob
After calculating it, I will post my calculation.

Thank you for your help sir

#### cikalekli

Joined Dec 10, 2020
103
Pretend the base is not connected and calculate the voltage at the junction. Then it is equivalent of a source at that voltage with a series resistor that us the parallel combination of the two.

Bob
Here I've just tried but confused.

#### cikalekli

Joined Dec 10, 2020
103

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#### ericgibbs

Joined Jan 29, 2010
12,932
hi cika,
I guess you know that when are using Thevinin in that way the voltage sources are considered as short circuits.

What do you make the junction voltage of the two resistors.??

Update: with the Base disconnected.!
E

#### cikalekli

Joined Dec 10, 2020
103
hi cika,
I guess you know that when are using Thevinin in that way the voltage sources are considered as short circuits.

What do you make the junction voltage of the two resistors.??

Update: with the Base disconnected.!
E
Hi Eric,
I must apply KVL right?

#### ericgibbs

Joined Jan 29, 2010
12,932
hi,
What do you make the junction voltage of the two resistors.??
Update: with the Base disconnected.!

Consider two resistors in series, one is 30K and the other 60k.
At the 30k end you have 5V and at the 60k end you have -1V, so what is the junction voltage.?

E