# applying KVL to semiconductor circuits

#### uzair

Joined Dec 26, 2007
110
just a simple question, is there any change in the KVL while we apply it in the circuits containing semiconductor devices like transistors or diodes? if someone can give a link it will also be a favour.

#### scubasteve_911

Joined Dec 27, 2007
1,203
As far as I know, KVL holds for semiconductors, whether it be a transistor or a diode. Obviously, voltage drops are dependent on currents, temperature, etc.

Maybe a specific example of what you are trying to solve?

Steve

#### uzair

Joined Dec 26, 2007
110
I am trying to apply KVL to the bi-polar junction transistor amplifier circuit.I want to calculate the values of amplified current or voltage through it.

#### hgmjr

Joined Jan 28, 2005
9,029
I believe one way to accomplish your goal would be to locate the appropriate transistor circuit model for your transistor such as the one to which I have linked.

hgmjr

#### uzair

Joined Dec 26, 2007
110
I have made my own circuit in which base-emitter junction is forward biased and collector-base junction is reverse biased.It is just a simple circuit.Can you tell me if there are some fundamental rules to apply KVL to semiconductor circuits?

#### uzair

Joined Dec 26, 2007
110
I have not learned KVL from this site.I have a different method of applying KVL.

#### hgmjr

Joined Jan 28, 2005
9,029
Can you provide a sketch showing how you apply KVL?

hgmjr

#### uzair

Joined Dec 26, 2007
110
Yes why not? First of all draw circuit diagram.Then choose the loop such that each resistance included at least once in the selected loops.Then assume a loop current in each loop such that all loop currents should be in the same direcion,clockwise or anticlockwise.Then write equations for all loops.For writing each loop equations, the voltage change across any component is positive if traversed from low to high potential and it is negative if traversed from high to low potential.Then solve the equations for unknown quantities.

#### hgmjr

Joined Jan 28, 2005
9,029
The document found at this link may give you a better idea of what I am talking about when I mentioned the need for a transistor circuit model.

hgmjr

#### uzair

Joined Dec 26, 2007
110
Figure 6 shows the circuit of which i am talking about.

#### hgmjr

Joined Jan 28, 2005
9,029
Figure 6 shows the circuit of which i am talking about.
That being the case, can you scroll down further and see how they apply transistor models to facilitate the circuit analysis?

Warning: Be sure to select between the DC model or the AC model based on the analysis you wish to perform.

hgmjr

#### uzair

Joined Dec 26, 2007
110
If there is any link which describes the KVL applied to semiconductor circuits, it can do the job.

#### hgmjr

Joined Jan 28, 2005
9,029
Take a look at figure 17 and look just below it for the KVL equations that apply.

hgmjr

#### uzair

Joined Dec 26, 2007
110
I do not understand how they have applied KVL in that link

#### hgmjr

Joined Jan 28, 2005
9,029
I do not understand how they have applied KVL in that link
Can you explain what you find unclear in their explanation?

hgmjr

#### uzair

Joined Dec 26, 2007
110
I just want to know some fundamentals of how to apply KVL to the semiconductor circuits.I am not an engineering student and i do not want to go very deep in this field.

#### hgmjr

Joined Jan 28, 2005
9,029
I suspect that one of the things that is causing you a bit of confusion is the concept of a dependent current source. You are probably more familiar with networks containing independent voltage sources and current sources and can solve those networks using KVL without any trouble.

If you are not familiar with solving networks containing dependent voltages and/or currents then you probably will want to get acquainted with them as a prerequisite to tackling the application of KVL to transistor models.

hgmjr

#### uzair

Joined Dec 26, 2007
110
I do not even know what are dependent voltage sources.Actually my physics and electronics study is extremely limited that is the root cause.As you said i would really like to get acquainted with them.

#### hgmjr

Joined Jan 28, 2005
9,029