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 General Electronics Chat Discussion forum for general chat about anything electronics related, including asking questions about material in the All About Circuits E-book, Worksheets, and Videos.

#1
12-26-2008, 06:17 PM
 Khalid Abur-Rahman Junior Member Join Date: Dec 2008 Posts: 34
DC and AC load line equations?

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?
#2
12-28-2008, 08:47 PM
 Thevenin's Planet Senior Member Join Date: Nov 2008 Location: portland ,Oregon Posts: 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.
#3
12-28-2008, 11:09 PM
 hgmjr Super Moderator Join Date: Jan 2005 Location: Tennessee, USA (GMT-6) Posts: 9,030 Blog Entries: 11

Here is a link to an article on bipolar junction transistors that has a short section on AC and DC load line analysis.

Check out Figure 4-34.

hgmjr
#4
12-29-2008, 12:32 AM
 Audioguru Banned Join Date: Dec 2007 Location: Ontario, Canada Posts: 9,411

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:
Attached Images
 sim transistor distortion..PNG (19.2 KB, 26 views)
#5
12-30-2008, 08:02 PM
 Thevenin's Planet Senior Member Join Date: Nov 2008 Location: portland ,Oregon Posts: 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.
#6
12-30-2008, 09:11 PM
 hgmjr Super Moderator Join Date: Jan 2005 Location: Tennessee, USA (GMT-6) Posts: 9,030 Blog Entries: 11

Quote:
 Originally Posted by Thevenin's Planet 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
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#7
12-30-2008, 09:19 PM
 hobbyist Senior Member Join Date: Aug 2008 Posts: 716 Blog Entries: 21

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.

 Related Site Pages Section Title Worksheet JFET amplifiers Worksheet Class A BJT amplifiers Worksheet Bipolar junction transistors in active mode Worksheet Simultaneous equations for circuit analysis Worksheet Th'evenin's, Norton's, and Maximum Power Transfer theorems Textbook ``Long'' and ``short'' transmission lines : Transmission Lines Worksheet Resonance Worksheet Time constant calculations Textbook The common-emitter amplifier : Bipolar Junction Transistors Textbook Active mode operation : Bipolar Junction Transistors

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