# DC and AC load line equations?

#### Khalid Abur-Rahman

Joined Dec 25, 2008
34
Can someone explain to me step by step how to plot and make transistor characteristics curves...? How do I go about drawing load lines and stuff?

R the many different lines on their for different values of rb?

#### Thevenin's Planet

Joined Nov 14, 2008
183
ploting a load line for a D.C. bias is lort of finding the D.C. Beta. Make a circuit in which you can vary the Base and the collector.Pick sone inteval (i.e. 1volt,2volt,3 volt,ect).As you move from volt to volt the collector voltage should not alter from some selective voltage when measuring the
base current and collector voltage and current.If the collector voltage changes adjust it through a "Pot" in the collector circuit.Continue the sequence until you have reached or almost reached the breakdown point on Base emitter.Once reaching the point adjust the Vcc to an higher voltage (for instance 2 volts) continue this process until the breakdown point is close.Every meadurement have to recorded.Once completed then the graph can be hand drawn.
A.C is smillar, but using a frquency of some sort.There is a device the can be use but you must have a ocilliscope which same a lot of restless time.

#### Audioguru

Joined Dec 20, 2007
11,251
I plotted load lines for transistors in school. Then I made circuits and the transistors didn't perform like the load lines. The transistors caused severe distortion when the levels were fairly high. A simulator shows the severe distortion like this:

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#### Thevenin's Planet

Joined Nov 14, 2008
183
Hi again!
I have this assumption that says that most mathematical formulas are only a approximation of the results,or a reminder regarding something important about subject. It save a large amount of trial and error. So that some small ajustment have to done to the finished product. There are does characteristics within the material or circuit that are not placed in the formulae.I have notice this in various calculations dealing with electronic equations. There is a very informable article in the electronic funamental 2 about DC/ac load line. ac load line analysis.I always would remember from high school that arithmetic is very exact.

To stand on the shoulder of others one must know what they know to reach farther.

#### hgmjr

Joined Jan 28, 2005
9,029
Hi again!
I have this assumption that says that most mathematical formulas are only a approximation of the results,or a reminder regarding something important about subject. It save a large amount of trial and error. So that some small ajustment have to done to the finished product. There are does characteristics within the material or circuit that are not placed in the formulae.I have notice this in various calculations dealing with electronic equations. There is a very informable article in the electronic funamental 2 about DC/ac load line. ac load line analysis.I always would remember from high school that arithmetic is very exact.
Can you indicate which electronic formula you believe to be an approximation?

hgmjr

#### hobbyist

Joined Aug 10, 2008
887
In electronics, formulas are almost always approximations, due to component tolerances, as well as other factors. You use the formulas to get you in the ballpark but it's the actual prototyping of a circuit that gets you the exact results.