You can buy a semiconductor curve tracer, assembled or in kit form.
Or you can build your own.

You can also build a computerized curve tracer with a couple of DACs and an ADC.

A curve tracer is very handy for checking transistors, diodes, zener diodes, tunnel diodes, etc.

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Pretty good and has two sockets if you want to get close to a matched pair.

Ron

 

The image you posted looks like it came from a Transistor Curve Tracer for example the old Tektronix 575. Anyway it is just a graphic plot.

Ron

I doubt it -- it's far too perfect. Looks like a prepared graphic illustration to me.

 

Is there a way to find this by hand? Do I need the resistance ahead of time? How do I figure out what resistance to use for the Q point taken from the load line? I am sorry if this seems dumb, I completely understand what the curves show but am confused how they are found when the base currents are included. Thanks again

Controlling the base current in an experimental setup is actually pretty easy. You know that the base-emitter voltage is pretty constant, so you can use a significantly higher voltage supply (the higher the better, but even 15 V will do pretty well) and then use a resistor between the base and the supply. You can either vary the resistance or, more convenient, vary the voltage. That results in a current source whose output impedance is the resistor you are using.

Let's say that you have a variable 0-15 V supply available and want 0.1 mA of base current. Use a 100 kΩ, 1% resistor and adjust the supply voltage to 10.7 V (assuming the emitter is at 0V). That will give you nominally 0.1 mA of base current. If the Vbe is actually only 0.5 V then you have 0.102 mA and if Vbe is 0.9 V you have 0.980 mA, assuming the resistor is dead on. So the uncertainty is about 2% and, with the resistor uncertaintly taken into account, still puts you within about 3% even over that wide a range of Vbe.

 

I wouldn't mind having that B&K if you could find a working one cheap. Somewhere around here, I have an old Military Transistor Tester in its hard shell field case that I picked up at a HamFest. If I can find it...

 

Here is a simple setup to test two terminal devices such as resistors and diodes.

https://forum.allaboutcircuits.com/...ge-supply-problems.127919/page-4#post-1049661

 

I doubt it -- it's far too perfect. Looks like a prepared graphic illustration to me.

Actually I have to agree it's not just perfect but it isn't green. Remember getting valves (tubes) and transistors as "matched pairs"?

Ron

Ron

 

I would like to eventually get a nice scope but are these curves necessary to obtain a load line and q-point? I have an exam and unfortunately most of the information was passed over or not explained thoroughly and I am worried I will need to construct a graph by hand or at least find the load line equation and/or q-point. Thanks again

 

Depends on the circuit. The reason why few datasheets include that graph is because while it is very helpful to aid initial understanding of how transistors behave, it has little practical utility in designing real circuits. In general, any circuit that would require the use of a load line like that to determine the operating point is probably a poorly designed circuit. This is not to say that knowing and understanding what a load line is or how to apply the concept has no value, but it's primary value is in understanding how and why circuits operate the way that they do.

So whether or not you need to do a load line to determine the operating point depends on the circuit you are given to analyze (or design). Most good circuits are largely immune to the significant variations in these parameters from one transistor to another and so they can be analyzed principally from the constraints forced on the transistor's operating point by the rest of the circuit.

 

I am worried I will need to construct a graph by hand

If it's a theory exam then you'd either be given the data you need or you would only be expected to draw an approximation of a characteristic curve.

 

I would like to eventually get a nice scope but are these curves necessary to obtain a load line and q-point? I have an exam and unfortunately most of the information was passed over or not explained thoroughly and I am worried I will need to construct a graph by hand or at least find the load line equation and/or q-point.

In close to a half-century of doing electronic design, mostly analog, I've never had the need to use any kind of load line analysis. Not even once.

And this is the reason:

The reason why few datasheets include that graph is because while it is very helpful to aid initial understanding of how transistors behave, it has little practical utility in designing real circuits.

Like @WBahn said, it's an aid to understanding. And little else.

 

I have also designed thousands of transistor circuits and have also NEVER used a load line. Instead I use the transistor's spec's on its datasheet and use Ohm's Law.
Usually you want the Q-point of a linear transistor so that it can cutoff and saturate with equal voltage swings, which is very simple to calculate.

 

I have been told about characteristic curves like this for a while but have never fully understood where they come from. I don’t see them on the datasheets, although they have a similar one where Ic and Ib are switched, and my books don’t really explain where they come from. Is this something I need to draw myself? If so where do I get the information required? Is it through testing the transistor on a meter or doing some math? Is the load line something I draw? Thanks in advance.

Learn what these mean, and how to do them yourself, easily:

Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3

 

OP you're right. I'm gettting more familar with transistor datasheets, but yeah I don't normally see those 3 variable graphs.

For a curve tracer, I recently made a nice stairstep generator with a binary counter, and a R2R network. In theory in outputs programable uA to a few mA currents. I built it and it works great but I need to choose the final parts to calibrate it to the actual output current numbers it should be, but it's pretty close.


Now I can use an old muli-tap transformer, or my signal gen, or us a tunable op-amp circuit I built, for the collector voltage sweep.