# Help with Thevenin equivalent

#### Ylich

Joined Apr 27, 2019
3
Hello, i am trying to get the thevenin equivalent between B an ground but i cant not find it. Thank you for the help

#### ericgibbs

Joined Jan 29, 2010
10,449
hi Ylich,
Welcome to AAC.
As this is a Homework assignment, please post your attempt at answering the question, we can then guide you through the problem.
E

#### Ylich

Joined Apr 27, 2019
3
Oh sorry, oke thanks. This is what i have got. I assume that i know the value of Rg, Vcc, R1, R2, an Vin(t); so i have 3 unknown values: Rth, V'in(t) and Vbias; then i have 3 unknown values and 2 equations, is that ok?. By the way, do you use any software to draw circuits?

#### Jony130

Joined Feb 17, 2009
5,180
Do you want do find the Rth for a AC signal or DC? Because DC-Voltage (Vcc) is short for an AC-signals.

#### Ylich

Joined Apr 27, 2019
3
Is there a method that gives you both in one? Can i use thevenin when the circuit mixes both dc and ac sources?

#### WBahn

Joined Mar 31, 2012
26,047
Is there a method that gives you both in one? Can i use thevenin when the circuit mixes both dc and ac sources?
Not really. The whole idea of a Thevenin equivalent requires that we be talking about a linear circuit. But the large signal behavior of most transistor circuits is very nonlinear. So what we normally do is treat the circuit as two circuits superimposed -- a DC circuit and an AC circuit with the excursions of the AC circuit being small enough that we can pretend it is linear, at least over the range of the excursions and at least to a degree that is acceptable for our purposes.

• Ylich