Hello,

Based on a video at:

http://www.youtube.com/watch?v=nSwq6TO6mTE

it shows how to get the Q point for a transistor. It also shows the transistor's characteristic curve so we can draw our load line.

However, when I open the datasheet for a PN2222 tarnsistor, I do not seem to find such a characteristic curve like the one shown in the video (or like the one in my attachment???)

Here are a couple of typical PN2222 data sheets...

http://www.auk.co.kr/pro_upload/PN2222_1.pdf
http://www.onsemi.com/pub_link/Collateral/PN2222-D.PDF

All I find is logarithmic curves if any at all??? So what should I do if I want to draw or plot a load line as shown in the video?

Thanks for all help?
r

 

You can create typical curve-tracer curves using LTspice. See the attachment.
Be aware that typical curves are just that. If you put a hundred PN2222s on a curve tracer, none will be identical, and none will look exactly like the simulation.

 

Hi Ron_H,

But why aren't these curves available in the spec ??? If one doesn't have LTspice, how is he supposed to trace a load line?

It seems LTspice is pretty popular... I was wondering is it a difficult program to learn for a newbie?

thanks

 

Hi Ron_H,

But why aren't these curves available in the spec ??? If one doesn't have LTspice, how is he supposed to trace a load line?

It seems LTspice is pretty popular... I was wondering is it a difficult program to learn for a newbie?

thanks

Load lines are seldom used by experienced designers. The datasheet usually has all the info you need to design an amplifier stage, a switch, or whatever.
The LTspice learning curve is pretty steep, and simulators are worthless, or worse, if you don't understand your circuit pretty well before you simulate it. Still, it won't hurt you to play with it, so long as you always keep in mind that garbage in=garbage out, or, in the case of simulators, garbage in=sophisticated garbage out.

 

Simply we don't need these curves do design amplifier circuit. Only in "circuit theory" people use these curves, real designer don't need them.

 

My 1968 Philips transistors databook has the curves that your video shows (is it a very old video?).

I studied load lines only in school, never in my career.
I forgot. The video is school stuff.

 

The LTspice learning curve is pretty steep, and simulators are worthless, or worse, if you don't understand your circuit pretty well before you simulate it. Still, it won't hurt you to play with it, so long as you always keep in mind that garbage in=garbage out,

humm... then i will wait a while ...

(is it a very old video?).

i don't think its an old video....

thanks guys!!

 

Transistor curve tracers and the curves they generate are mainly used to analyze transistor characteristics. They give a snapshoot of how a typical transistor works for varying values of current and voltage. The curves are seldom used to design circuits since, for good design practice, you don't use typical characteristics, you design the circuit to operate with worst-case values.