BJT Characteristic Curves !?HELP?! - Page 1
Forum section: electronics / beginners

author: shanecy
author_rank: Contributor
timestamp: July 14, 2013, 04:51:54 pm
content: I'm learning about bipolar junction transistors and I'm trying to understand from my text on how to build a graph with characteristics curves. Currently all I can understand at this point is the graph is comparing three variables Ic, Vce, and Ib.I've reviewed tutorials and thoroughly have reviewed my textbook. The tutorials/textbook have been hard to follow and having another perception/explanation from one of you may be beneficial to me.To be as specific as possible in what my questions are I am listing them below. I understand the questions may be to general in nature and if pushing me in the direction of another online source is easier I would equally appreciate it.What is the purpose of a graph containing characteristic curves for a BJT?What relation or effect should I understand about Ic, Ib, Vce?If I was to build a graph of characteristic curves what information would need to be present?What would be a rough outline on the procedure in building a graph? For example, step one.....step two.. and so on.If the load line contains two extremes, one extreme being when Ic is 0A and one extreme when Vce is 0V, how do I derive the ordered pair of each extreme to graph the load line? What is this load line entailing and what does the Q specifically represent?

author: Bored@Work
author_rank: Super Contributor
timestamp: July 14, 2013, 07:38:51 pm
content: Sounds pretty much like homework. There isn't anything more to it than what is given in the textbooks. If you think your textbook is hard to follow then you probably missed some basics earlier on.

author: hlavac
author_rank: Frequent Contributor
timestamp: July 14, 2013, 07:41:19 pm
content: This is a bit too academic for a practical hobbyist like me, but let me try:What is the purpose of a graph containing characteristic curves for a BJT?They describe how the device behaves under specified range of conditions.From these graphs you can find suitable working conditions for BJT in your design.They may be considered a model of the device to be used in calculations.What relation or effect should I understand about Ic, Ib, Vce?Usually certain Ib and temperature sets certain Ic vs Vce curve. This is a bit hard to understand because they draw it as a 2D graph using several fixed Ib samples to draw several Ic,Vce curves.In reality think of it as a 3D surface with Ib as depth for a given temperature (that adds another dimension to it...)If I was to build a graph of characteristic curves what information would need to be present?There are several possible graphs you can draw about BJT that are some projection slices of the space of Ib, Vbe, Ic, Vce, temperature, transition frequency, allowed power dissipation...Look at some BJT datasheets for what combinations are important.Usually temperature is assumed to be 25 degrees C to cut down on the dimensionsWhat would be a rough outline on the procedure in building a graph? For example, step one.....step two.. and so on.These graphs are 2D projections (slices) of multidimensional characteristic "surface".They are constructed by fixing all but two of the parameters and plotting the relations between the remaining two in a 2D graph by sweeping one and measuring other.There is special kind of measurement equipment called Curve tracer that automates the process of sweeping the parameters and plotting the relations.It looks like an oscilloscope with built in sweeping current/voltage generators.If the load line contains two extremes, one extreme being when Ic is 0A and one extreme when Vce is 0V, how do I derive the ordered pair of each extreme to graph the load line? What is this load line entailing and what does the Q specifically represent?You lost me there